25 hypertensive subjects underwent a double-blind, randomized study to compare the effects of ticrynafen (TCNF) with hydrochlorothiazide (HCTZ) on blood pressure (BP), renal function, serum uric acid (UA) and electrolytes, and body fluid spaces. BP was similarly lowered by TCNF and HCTZ. Neither TCNF nor HCTZ had a significant effect on true or regular creatinine, inulin, or PAH clearances. TCNF lowered UA, whereas HCTZ elevated UA. Both produced similar electrolyte disturbances. Neither TCNF nor HCTZ, according to our methods, had a significant effect on plasma volume, extracellular fluid, or total body water. The primary advantage of TCNF compared with HCTZ is its profound hypouricemic effect.