Plasma concentrations of pirprofen and of its pyrrol metabolite were assessed in 9 elderly patients (3 males, 6 females; mean age 76 years) suffering from chronic degenerative disease. Pirprofen 400 mg in 4 ml was administered i.m. and the pharmacokinetic profile of the drug and the metabolite was calculated. The AUC, Cmax and t1/2 of pirprofen were similar to those found in previous studies, and, as expected, those parameters for the pyrrol metabolite were lower (Cmax = 2.8 micrograms/ml-1; tmax = 6.4 h; AUC(0-32) = 56.5 micrograms.h.ml-1). One patient (n = 8) showed different pharmacokinetic behaviour, which is discussed. The data suggest that age has little influence on the pharmacokinetic of pirprofen, although unpredictable responses should always be considered in clinical practice.