The analgesic activity of diflunisal was evaluated through the measurement of cutaneous sensory and pain thresholds after electrical stimulation. Twelve healthy volunteers were examined at baseline and five hourly intervals after oral administration of 500 mg and 1 gm of diflunisal. The results showed that the sensory threshold was not modified by diflunisal, but that the pain threshold was significantly increased two and three hours after 500 mg of diflunisal and one, two, and three hours after 1 gm of diflunisal. At two hours the pain threshold was significantly higher after 1 gm than after 500 mg of diflunisal. It is concluded that diflunisal produces an actual increase of the pain threshold in healthy human subjects and that the amplitude, latency, and duration of its effect are dose related.