The influence of vitamin C on the pharmacokinetics of antipyrine was investigated in eleven elderly men aged 65-74. Antipyrine (15 mg kg-1) was administered intravenously on three separate occasions over a 7-week period: (a) before dietary vitamin C restriction, (b) after approximately 5 weeks of dietary vitamin C restriction, and (c) after 2 weeks of vitamin C supplementation (500 mg orally twice daily). The mean plasma and leucocyte vitamin C levels (+/- S.D.) before vitamin C restriction were 1.26 +/- 0.31 mg dl-1 and 26.6 +/- 6.7 micrograms 10(-8) leucocytes, respectively. These values decreased and then increased significantly following vitamin C restriction and supplementation, respectively. The mean plasma half-life of antipyrine was 10.2 h and the mean plasma clearance was 2.561 h-1 1.73 m-2 before vitamin C restriction. No significant changes in the clearance, volume of distribution, or half-life of antipyrine occurred during the study, indicating that short-term alterations in vitamin C intake do not affect the pharmacokinetics of antipyrine in elderly males.