This randomized, double-blind, placebo-controlled, cross-over study will evaluate the glucose concentration and other glycemic parameters of efficacy, and the safety and tolerability and pharmacokinetics of single oral doses of RO4998452 in patients with diabetes mellitus type 2. On 3 treatment days a week apart, patients will each receive orally one of 2 dose levels of RO4998452 or placebo. Anticipated time of study treatment is 3 weeks. Target sample size is <50.