Teriflunomide Male Transmission Study

Inclusion Criteria: 1. Males with relapsing forms of multiple sclerosis appropriately treated with teriflunomide 14 mg po daily; 2. Continuous treatment for three months with good compliance as assessed by the investigator 3. Age between 18 and 55 4. Penile-vaginal intercourse with a female partner at least twice a month with unimpeded ejaculation. 5. Compliance with safety assessments, e.g., regular bloodwork for complete blood count and liver function testing as recommended in the Package Insert 6. Able to give informed consent Females 1. Regular sexual intercourse with a male partner who is actively taking teriflunomide 2. Age between 18 and 55 3. Able to give informed consent 4. Negative urine pregnancy test at the time of blood sampling 5. Reliable contraception that does not involve barrier methods Exclusion Criteria: 1. Use of barrier methods of contraception 2. For males, contraindications to the continued use of teriflunomide 3. Couples that are actively trying to conceive 4. For males, noncompliance with teriflunomide therapy 5. Inability or unwilling to give consent or comply with the protocol 6. Pregnancy of the female sexual partner.