Study to Investigate Dose-related Efficacy of LAS41004 in the Treatment of Psoriasis

Inclusion Criteria: * Male or female patients between 18 and 75 years of age with a diagnosis of stable plaque-type psoriasis (psoriasis vulgaris) for at least 6 month * Psoriasis plaques that are suitable to be defined as target area lesions by the following criteria: 1. Psoriasis plaques must be located at trunk and/or extremities. Plaques that are located on the head (incl. scalp), palms, sole of the feet, intertriginous or genitoanal areas are not suitable as target areas 2. Comparable psoriasis plaques with at least "2" in each score (Range 0-4) for the three distinct symptoms scaling; erythema; and induration 3. No more than 3 points difference in total score (= sum of scores for scaling, erythema and induration; Range 0-12) of the chosen comparable psoriasis plaques 4. Enough psoriatic surface area to define 8 clearly distinguishable (minimum distance between test areas: 1cm) test areas of at least 1 cm² plaque size * Patient is willing and able to comply with the requirements of the clinical study protocol. In particular, patient must adhere to concomitant therapy prohibitions of the test areas and must agree to avoid intense UV exposure of the test areas during the study * Written informed consent to participate in the study, prior to any study related procedures, indicating an understanding of the purpose of the study * A patient of childbearing potential agrees to use one of the following contraceptive methods for the duration of the study: 1. Strict abstinence (exception: male partner with a vasectomy for at least 3 months prior to study entry is allowed) 2. Combined oral, implanted or injectable contraceptives on a stable dose for at least 3 months prior to study entrance 3. Intrauterine device (IUD) inserted for at least 1 month prior to study entrance Exclusion Criteria: * Too few body surface area covered with psoriasis plaques that meet the specified inclusion criteria to be defined as 8 clearly distinguishable test areas * Any condition that may interfere with the study assessments or sonographic measurements of the skin and/or may have an influence on skin immune response (incl. open wounds) * Known adverse reactions of any severity or hypersensitivity to any ingredient of the test products * No willingness to avoid induction of heavy sweating, e.g. due to sauna visits, excessive sports activities during the study course * No willingness to avoid swimming, bathing or wetting of the designated test areas between visits * Pregnant or breast-feeding women * A medical condition that may put the patient at a general risk and therefore would prevent participation in the clinical trial (including but not limited to: serious infectious diseases, major surgery within the last 4 weeks, coronary artery disease, renal impairment, hepatic impairment, uncontrolled metabolic diseases, disorders of the calcium metabolism, autoimmune diseases) * History or presence of malignant disease (other than surgically removed basal cell carcinoma) and/or auto immune diseases * Current diagnosis of guttate, erythrodermic or pustular psoriasis * Patients who did not respect the following wash-out periods prior or during the study