Dihydropyrimidine dehydrogenase (DPD) is the major metabolic enzyme in the catabolism of 5-fluorouracil, and the activity in normal tissues shows a wide variation among individuals. Recent studies demonstrate the relevance of DPD in the pharmacokinetics, toxicity, and antitumor efficacy of 5-fluorouracil. We investigated the DPD activity in peripheral blood mononuclear cell form 114 healthy subjects in Korea. The DPD activities in healthy volunteers were shown to follow a unimodal distribution. The mean of the activity was 0.28 ± 0.16 nmol/min/mg protein. A wide (13-fold) intersubject variability was observed (range, 0.06-0.80 nmol/min/mg protein), and, on average, DPD activity in women (0.26 ± 0.14) was 13% lower than in men (0.30 ± 0.16). These findings indicate that the activity of DPD in this study was higher than in reports of research with French and white American populations.