The aim of the study was to evaluate a possible chronokinetic phenomenon of ketoprofen administered orally and by continuous intravenous infusion. In the first part of the study, ketoprofen was administered orally to 8 healthy male volunteers aged between 25 and 45 years, at a dose of 2 X 50 mg at 7:00 a.m. (time I), 1:00 p.m. (time II), 7:00 p.m. (time III) and 1:00 a.m. (time IV), on the same day of the week at an interval of 2 weeks, during the first three months of the year. The order of administration was randomised, each subject acted as his own control and received ketoprofen at the four times mentioned above. A total of 14 venous blood samples were taken over 12 hours. The results indicate that the maximal serum concentration (Cmax) was significantly higher at time I (13.4 +/- 14.1) than at times II, III and IV (6.9 +/- 1.1, 7.2 +/- 0.7, 6.4 +/- 0.5 mg/l) (p less than 0.01). The time required to reach this concentration (Tmax) was significantly longer for time IV (135.0 +/- 16,8) than for times I, II and III (73,1 +/- 14.1, 75,0 +/- 16.6; 82.5 +/- 12.7 minutes) (p less than 0.05). The excretion half-life (t 1/2B) was significantly longer for time IV (4.3 +/- 0.6) than for times II and III (2.8 +/- 0.5, 2.5 +/- 0.2 hours) (p less than 0.05). Statistically significant differences were also observed in the area under the curve measured at midday (AUC 12) and in the total clearance (CIT) for the various sample times.(ABSTRACT TRUNCATED AT 250 WORDS)