To evaluate the potential contribution of prostaglandins (PGs) and thromboxane (TX) to the development of chronic glomerulonephritis, we measured the urinary excretion of PGE, PGF2 alpha, 6-keto-PGF1 alpha and TXB2 by radioimmunoassay in 36 patients with chronic glomerulonephritis. In patients with nephrotic syndrome, urinary excretion of PGE and TXB2 was highly increased, whereas that of PGF2 alpha and 6-keto-PGF1 alpha remained normal. In patients with non-nephrotic chronic glomerulonephritis, urinary excretion of TXB2 was significantly increased, whereas that of PGE and 6-keto-PGF1 alpha remained normal and that of PGF2 alpha was significantly decreased. In patients with chronic renal failure, the urinary excretion of all PGS and TX was markedly decreased presumably due to a decrease in the number of cells which can metabolize arachidonic acid. These results suggest that TXA2 plays an important role as an exaggerating factor in the development of chronic glomerulonephritis, particularly that accompanying nephrotic syndrome, and that renal synthesis of PGE is compensatorily increased to maintain renal function in nephrotic syndrome.