This is a double-blind (neither physician or participant knows the name of the assigned study drug), placebo-controlled (substance containing no medication), study in male and female volunteers with type 2 diabetes mellitus. For each volunteer, the study consists of a screening phase (up to 45 days), a run-in phase during which volunteers discontinue their oral anti-hyperglycemic drugs (21 to 35 days), a treatment phase during which volunteers will continue to be off their anti-hyperglycemic drugs and receive daily study drug (JNJ-38431055 or placebo) for 14 days, and a follow-up phase (10 days). After the follow-up phase, volunteers will restart their oral anti-hyperglycemic drugs. The following safety evaluations will be taken throughout the study: Electrocardiogram (an ECG is a painless procedure that gives a picture of the electrical activity of the heart), blood pressure, heart rate, and blood samples for laboratory tests. The primary outcomes will be safety and tolerability of JNJ-38431055 and 24-hour weighted mean glucose concentrations after 14 days of dosing with JNJ-38431055. Study drug will be administered as daily doses for 14 days. The two treatments will be JNJ-38431055 and placebo.