Study to Evaluate Handling Errors in Usage of SERETIDE® Metered Dose Inhaler (MDI) (EVOHALER®) by Adult Subjects Currently Using the SERETIDE DISKUS® Inhaler

Inclusion Criteria: * \>=18 years of age at the time of informed consent. * A diagnosis of asthma as defined by the National Institutes of Health, 2007. * Must be currently treated with SERETIDE via the DISKUS Inhaler and have been maintained on this dose for 3 months prior to Visit 1. * Have controlled asthma defined as a total ACT score \>= 20 * Must be able to use their DISKUS inhaler correctly. Correct use is defined as making no critical errors during the assessment of DISKUS inhaler use at Visit 1. * Male * Female subject is eligible to participate if she is not pregnant (as confirmed by a negative urine human chorionic gonadotrophin \[hCG\] test), not lactating, and at least one of the following conditions applies: 1. Non-reproductive potential defined as: Pre-menopausal females with one of the following; documented tubal ligation, documented hysteroscopic tubal occlusion procedure with follow-up confirmation of bilateral tubal occlusion, hysterectomy, documented bilateral Oophorectomy. Postmenopausal defined as 12 months of spontaneous amenorrhea (in questionable cases a blood sample with simultaneous follicle stimulating hormone \[FSH\] and estradiol levels consistent with menopause). Females on hormone replacement therapy (HRT) and whose menopausal status is in doubt will be required to use one of the highly effective contraception methods if they wish to continue their HRT during the study. Otherwise, they must discontinue HRT to allow confirmation of post-menopausal status prior to study enrolment. 2. Reproductive potential and agrees to follow one of the options listed below in the GSK modified list of highly effective methods for avoiding pregnancy in females of reproductive potential (FRP) requirements from 30 days prior to the first dose of study medication and until after the last dose of study medication and completion of the follow-up contact. GSK modified list of highly effective methods for avoiding pregnancy in FRP: a. Contraceptive subdermal implant that meets the standard operating procedure (SOP) effectiveness criteria including a \<1percent rate of failure per year, as stated in the product label. b. Intrauterine device or intrauterine system that meets the SOP effectiveness criteria including a \<1 percent rate of failure per year, as stated in the product label. c. Oral Contraceptive, either combined or progestogen alone. d. Injectable progestogen. e. Contraceptive vaginal ring. f. Percutaneous contraceptive patches. g. Male partner sterilization with documentation of azoospermia prior to the female subject's entry into the study, and this male is the sole partner for that subject. h. Male condom combined with a vaginal spermicide (foam, gel, film, cream, or suppository). GSK modified list of highly effective methods for avoiding pregnancy in FRP does not apply to FRP with same sex partners, when this is their preferred and usual lifestyle or for subjects who are and will continue to be abstinent from penile-vaginal intercourse on a long term and persistent basis. These allowed methods of contraception are only effective when used consistently, correctly and in accordance with the product label. The investigator is responsible for ensuring that subjects understand how to properly use these methods of contraception. * Capable of giving signed informed consent which includes compliance with the requirements and restrictions listed in the consent form and protocol. Exclusion Criteria: * Have a current diagnosis of chronic obstructive pulmonary disease (COPD) * Have experienced an asthma exacerbation within 3 months of Visit 1 or a lower respiratory tract infection within 6 weeks of Visit 1. An exacerbation is defined as worsening asthma requiring any treatment other than rescue salbutamol. This includes requiring the use of systemic or inhaled corticosteroids and /or emergency room visit or hospitalisation. * Other Concurrent Diseases: A subject must not have any clinically significant, uncontrolled condition or disease state (such as severe cardiovascular disorders or heart rhythm abnormalities, diabetes mellitus, thyrotoxicosis, uncorrected hypokalaemia or predisposition to low levels of serum potassium) that, in the opinion of the investigator (in consultation with the GSK Medical Monitor if required), would put the safety of the subject at risk through study participation or would confound the interpretation of the results if the condition/disease exacerbated during the study. Please refer to the SERETIDE Product Label for a full list of conditions for special warnings and precautions for use. * Currently taking potent Cytochrome P450 3A4 (CYP 3A4) inhibitors * Currently taking beta-blockers (selective and non-selective). * Allergic to salmeterol, fluticasone propionate or to norflurane (HFA 134a) or to any other excipients. * The subject has participated in a clinical trial and has received an investigational product within the following time period prior to the first dosing day in the current study: 30 days, 5 half-lives or twice the duration of the biological effect of the investigational product (whichever is longer). * Exposure to more than 4 investigational medicinal products within 12 months prior to the first dosing day.