Kinetics of ketoprofen release in man from a sustained-release preparation (150 mg) and from capsules (3 X 50 mg) were studied comparatively in 10 healthy adults. Bioavailability of the slow-release preparation is similar to that of capsules : surfaces under the serum concentration curves and urinary elimination were found to be identical. In the sustained-release preparation the immediately available layer (75 mg) ensures achievement of maximal serum concentrations amounting to 59% of those obtained with capsules, after the same time interval. The slow-release layer (75 mg) produces higher serum concentrations from the third hour on, justifying administration of the formulation in two daily doses.