Nine volunteers were dosed once daily for 15 days with a controlled release formulation of ketoprofen. The peak plasma ketoprofen concentration (4.2 micrograms/ml) and apparent elimination half-life (8.4 h) did not markedly alter during the course of the study. Plasma ketoprofen concentrations at 24 h after dosing were 0.79 micrograms/ml. These minimum ketoprofen concentrations suggest that this formulation is suitable as a once daily dosing regimen.