This double-blind, randomized, placebo-controlled, 2-Part study will evaluate the pharmacokinetics and safety of RO4917523 in healthy Japanese and Caucasian volunteers. In Part 1, healthy Japanese volunteers will be randomized to receive 2 oral doses of either RO4917523 or placebo, with a washout period of 21 days between dosing. In Part 2, healthy Japanese and Caucasian volunteers will be randomized in cohorts to receive either RO4917523 or placebo orally daily for 14 days.

Inclusion Criteria:

• Healthy Japanese (Part 1 + 2) or Caucasian (Part 2) adults, 18- 50 years of age
• Japanese subjects must have Japanese parents and grandparents who were born in Japan
• Caucasian subjects must have 4 Caucasian grandparents
• Body mass index (BMI) 18.5 to 26 kg/m2, and a body weight of at least 45 kg
• Non-smoker for at least 90 days prior to dosing Day 1

Exclusion Criteria:

• Participation in a clinical trial with an investigational drug within 90 days prior to dosing Day 1. (Volunteers having participated in Part 1 will not be allowed to participate in Part 2 and vice versa)
• History or evidence of any clinically significant disease or disorder
• Pregnant or lactating women
• Positive for hepatitis B, hepatitis C or HIV
• Positive drug screen test, positive cotinine test and/or positive alcohol test
• Any confirmed significant allergic reactions to any drug, or multiple allergies in the judgement of the investigator