The pharmacokinetics of ketoprofen following the administration of the first and final dose of a controlled release formulation (200 mg ketoprofen) once daily for 10 days to nine elderly patients have been studied. Plasma ketoprofen concentrations were measured by h.p.l.c. The data were compared to previously reported studies in young male volunteers. Mean +/- s.d. peak plasma concentrations (5.6 +/- 1.75 micrograms ml-1 and 6.3 +/- 2.7 micrograms ml-1 on day 1 and day 10, respectively) were higher than those reported in young volunteers given similar treatment, but similar to those reported in young volunteers following 50 mg four times daily of conventionally formulated ketoprofen, and markedly lower than reported following a single 100 mg dose of ketoprofen. The half-life for drug release (mean +/- s.d.) from the controlled release formulation (8.5 +/- 7.4 h) and accumulation upon repeated dosing (28%) were essentially the same as reported for young volunteers. The area under the plasma concentration-time curve was about 65% greater than reported in young volunteers following administration of controlled release ketoprofen. This increase in exposure to ketoprofen is probably partly due to the lower volume of distribution in the elderly and partly due to a reduced renal excretion of the glucuronide metabolite of ketoprofen. It was concluded that controlled release ketoprofen may be administered in standard doses (200 mg once daily) to elderly patients whose elimination processes are not severely impaired (i.e. severe renal failure or hepatic disease).(ABSTRACT TRUNCATED AT 250 WORDS)