Renal albumin excretion rate was 7.3 mg/24 h (SEM 0.5, range 0.6-21.0) in 66 healthy subjects. This rate increased markedly during and shortly after strenuous exercise on a bicycle ergometer (before: 5.5 +/- 0.6 micrograms/min; during and just after: 16.9 +/- 2.2 micrograms/min; P less than 0.001; n = 30). However, albumin excretion/24 h was not significantly higher during 24 h with a period of strenuous exercise than during 24 h without such exercise (10.3 +/- 0.9 mg/24 h vs 8.5 +/- 0.7 mg/24 h).