In view of the possible role of prostaglandins (PG) and thromboxane (TX) in the disturbances of renal function and blood flow after the injection of diatrizoate into the renal artery, we have determined the levels of PGE2, 6-keto-PGF1 alpha (a stable metabolite of prostacyclin) and TXB2 in the renal venous blood before, during and after renal arteriography in 12 patients. Radioimmunologically assayed PGE2 was the most abundant prostaglandin in renal venous blood. Lower basal levels of PGs were associated with renal adenocarcinomas or other tumours than non-tumour kidneys. The concentrations of 6-keto-PGF1 alpha and PGF2 alpha rapidly increased after diatrizoate injection and returned to the basal levels within 5 minutes. Slower elevation was noticed in the PGF2 level of 5 tumour kidneys. Renal plasma concentration of TXB2 remained unchanged throughout the study. The rapid elevation of renal venous prostacyclin and PGF2 alpha concentration after the contrast injection may reflect the enhanced intrarenal prostaglandin synthesis or may be secondary to hemodynamic changes in the kidney caused by hypertonic diatrizoate.