This placebo-controlled, randomized, observer-blind, dose-ascending study will investigate the safety, tolerability, pharmacokinetics and pharmacodynamics of single and multiple doses of RO5271983 in healthy volunteers. Healthy volunteers will be randomized to receive either a single oral dose of RO5271983 or placebo in the SAD part or multiple oral doses of RO5271983 or placebo in the MAD part. The anticipated time on study treatment is approximately 14 weeks for the SAD part and up to 8 weeks for the MAD part.