Male volunteers were infused with L-arginine dextran and Haemaccel. Arginine (0.5 g/kg body weight infused over 30 min) resulted in transient highly significant increases in urinary albumin (p less than 0.001), beta 2-microglobulin (p less than 0.001) and N-acetyl-beta-D-glucosaminidase [NAG] (p less than 0.001). These effects lasted less than 120 min. Dextran 40 and 70 (500 ml infused over 2 h) did not affect urinary albumin, beta 2-microglobulin or NAG excretion. Haemaccel (8 ml/kg body weight infused over 2 h) resulted in significant increases in urinary albumin (p less than 0.05) and beta 2-microglobulin (p less than 0.01) during the second hour of the infusion. It also caused a biphasic increase in urinary NAG excretion, the initial peak (p less than 0.05) coinciding with the peak of albumin and beta 2-microglobulin excretion. The second peak which was more defined (p less than 0.01) occurred 21-24 h after the beginning of the infusion. Neither arginine or Haemaccel have been reported to be nephrotoxic whereas dextran infusions are a well recognised cause of acute tubular necrosis. These data indicate that increases in urinary beta 2-microglobulin and NAG are not always reliable indicators of nephrotoxicity or renal tubular cell damage.