Experiments were designed to test the possibility that glomeruli can convert angiotensin I (AI) to angiotensin II (AII) (Thurau, Dahlheim & Granger, 1969). In six experiments, 10 μg (1-asp-5-ile) AI in 1·1 ml 0·15m-phosphate—saline buffer, pH 5·7, were incubated in stoppered neoprene tubes with 20–25 glomeruli dissected as previously described (Brown, Davies, Lever, Parker & Robertson, 1965) from kidneys of New Zealand White rabbits. The glomeruli were stored frozen, then thawed and incubated. In 2 control experiments AI was incubated with the paper fragments used to transfer glomeruli to the incubation tube, in 1 control experiment with 25 boiled glomeruli, and in 4 control experiments with rabbit blood (0·1 μl) equal in volume to 25 glomeruli (Vimtrup, 1928). In another control experiment glomeruli were incubated without angiotensin. Ten μg AI were incubated with buffer alone with each set of experiments. An incubation pH of 5·7 was chosen because single