Plasma concentrations of the enantiomers of flurbiprofen were measured following oral administration of (S)-flurbiprofen 50 mg and (R)-flurbiprofen 50 mg and 100 mg to sixteen healthy subjects. Chiral inversion did not occur to a measurable extent. Significantly higher values of AUC (55.2 +/- 17.0 vs 44.6 +/- 11.2 micrograms ml-1h) elimination half-life (5.6 +/- 1.4 vs 4.0 +/- 1.0 h) and mean residence time (7.5 +/- 1.6 vs 5.7 +/- 1.2 h) were observed after 50 mg (S)-flurbiprofen as compared with 50 mg (R)-flurbiprofen. With the exception of Cmax and AUC values pharmacokinetic data for the 50 mg and the 100 mg dose of (R)-flurbiprofen did not differ significantly. The data are of clinical relevance if (R)-flurbiprofen also has analgesic activity in humans and is to be developed as an analgesic.