The pharmacokinetics and effects of creatine and caffeine administration on anaerobic and aerobic performance of 7 trained athletes were studied in a randomized, placebo-controlled, double-blind crossover design. The treatments were: placebo (PLA), a single oral dose (7 mg x kg(-1)) of caffeine (CAF), repeated oral doses (3 x 100 mg x kg(-1) x day(-1)) of creatine for 3 days (CRE), or the combination of caffeine and creatine (CAF + CRE) before physical exercise. In one session CAF was administered without exercise. Drug administration was followed by 3 repetitive 1-minute exercise bouts on a bicycle ergometer at maximal speed (anaerobic exercise) starting 70 min after drug administration. Anaerobic exercise was followed by 45 min of cycling at constant pedalling speed and workload (aerobic exercise). CRE and CAF, alone or in combination, did not improve maximal pedalling speed (rpm), maintenance of maximal speed (rpm) or total work output (kJ) during the 1 -minute bouts, when compared with PLA. In addition, no statistically significant differences in heart rate or blood lactate were observed between the treatments either during anaerobic or aerobic exercise bouts. Creatine was rapidly and efficiently absorbed, as reflected by plasma concentrations. The mean +/-SEM value for creatine Cmax was 1.22+/-0.14 mmol x l(-1), tmax 92+/-7 min and plasma half-life (t1/2beta) 172+/-21 min. Caffeine pharmacokinetics were not affected by concomitant administration of creatine or by physical exercise. In conclusion, neither maximal performance and subsequent recovery nor aerobic performance were enhanced by oral creatine supplementation in the study.