This single-center, open label, randomized, 3-period cross-over study will compare 3 modified-release formulations of RO4917523 in healthy volunteers. Subjects will be randomized to one of six sequences to receive single oral doses of RO4917523 slow, target and fast release modified release (MR) capsules along with a reference intravenous microdose with the target capsule. A washout period of at least 21 days will occur between treatments.

Inclusion Criteria:

• Healthy male and female volunteers, 18 - 55 years of age inclusive Healthy status will be defined by absence in evidence of any active or chronic disease following a detailed medical and surgical history and a complete physical examination
• Body mass index (BMI) of 18 to 30 kg/m2, inclusive, and body weight of at least 50 kg
• Females of child-bearing potential must agree to use effective contraception as defined by protocol
• Non-smoker for at least 90 days prior to dosing on Day 1

Exclusion Criteria:

• History or presence of a clinically significant psychiatric condition as defined by protocol
• Participation in an clinical study with an investigational drug within 60 days or 5 times the half-life (whichever is longer) preceding first administration of study drug. Participation in more than 3 other drug studies within 10 months preceding first administration of study drug.
• Clinically significant disease or disorder
• Personal or family history of long QT syndrome or sudden death
• Any suspicion or history of alcohol and/or other substance abuse or dependence in the last 6 months
• Subject likely to need concomitant medication during the study (including for dental conditions), except for hormonal contraception or HRT
• Pregnant or lactating women, or women who intend to become pregnant during the course of the study
• Positive for hepatitis B, hepatitis C or HIV infection
• Any confirmed significant allergic reactions against any drug, or multiple allergies