Twenty-four cases of gouty and non-gouty hyperuricaeima have been treated with 50 to 300 mg daily doses of benzbromarone during periods of 4 to 150 days. Benzbromarone showed a dramatic, fast and reliable hypo-uricaemic effect in all cases. This effect was more pronounced in non-gouty than in gouty individuals. Tolerance of benzbromarone at this dose level is good, except for rare instances of digestive uneasiness and the occurrence of gouty attacks during treatment in three cases. Benzbromarone is primarily an uricosuric agent; its effect is different from that of known uricosuric agents and moreover, does not account for the whole hypo-uricaemic effect.