A simple and reliable HPLC method for the determination of tienilic acid ((TA) Selacryn, Selcryn, Diflurex, Ticrynafen) and its alcoholic metabolite in plasma and urine has been developed. In 8 healthy adult volunteers the plasma and urinary levels of tienilic acid and its alcoholic metabolite, and plasma and urinary levels of sodium, creatinine and uric acid were measured after oral administration of tienilic acid 250 mg. The pharmacokinetic parameters found differed only slightly from those reported in the literature, as there was faster absorption and a shorter half-life. TA is probably excreted by a saturable renal tubular transport mechanism. The pharmacodynamic effects of tienilic acid developed quickly, the uricosuric effect being very impressive and the natriuretic effect moderate. These effects disappeared in about 8 h. An inverse relationship was found between the starting plasma uric acid level in an individual and the maximal uric acid clearance - the higher the plasma uric acid level, the lower was the maximum effect. Plasma tienilic acid level and natriuretic effect were correlative within individuals and intra-individually (p less than 0.05). Urinary tienilic acid level and natriuretic effect were correlated, too (p less than 0.05 to p less than 0.001), but only intraindividually. No correlation between drug level and uricosuric effect was found.