A study was carried out in 10 healthy male subjects to investigate whether mofebutazone, a phenylbutazone derivative, influenced furosemide-induced diuresis and PGE2 excretion as has been shown with other non-steroidal anti-inflammatory agents such as aspirin and indomethacin. The subjects received, at random, a single dose of either 40 mg furosemide or 40 mg furosemide plus 600 mg mofebutazone and were then crossed over to the other regimen after 10 days. Urine was collected for 45 minutes before and then for six 45-minute clearance periods after drug administration. Urine volumes and excretion of sodium, potassium, chloride, magnesium, creatinine and the main metabolite of PGE2 were measured at the end of each period, as were blood levels of creatinine and mofebutazone from samples taken before, during and after administration. The results showed no significant differences between the two groups, indicating no interaction between mofebutazone and the diuretic.