Two separate studies were performed: in the first study for healthy male volunteers received three single oral doses (150, 250 and 400 mg) of 5-methylpyrazine carboxylic acid 4-oxide (acipimox) according to a randomized sequence. Plasma levels of the drug were determined by RIA and urinary excretion by HPLC. In the second trial the effect of food on the drug bioavailability and pharmacokinetics during repeated administration was investigated in six volunteers. The RIA method was adopted to measure plasma and urine levels. Acipimox was rapidly and almost completely absorbed after the three single doses. About 90% of the administered dose was recovered as unchanges drug in urine collected up to 24 h. Peak plasma levels, area under plasma levels curves and urinary excretion were linearly related to the administered dose. The presence of food in the gastro-intestinal tract did not adversely affect the bioavailability of the drug. No significant changes were noted in the rate of elimination after 6 days of treatment with 250 mg t.i.d. Plasma levels determined after the 19th dose were in good agreement with those predicted on the assumption of linear pharmacokinetics and a one-compartment open model, with a half-life of about 2 h.