Glomerular filtration rate (GRF) as measured by inulin clearance and renal plasma flow (RPF) as measured by PAH clearance were determined in 9 mountaineers before and during suspension. The two step permanent infusion technique was employed for 3 periods of 8 min. GRF decreased from 123.0 +/- 14.9 ml/min to 25.3 +/- 3.9 ml/min and RPF from 791.0 +/- 101.0 ml/min to 129.0 +/- 20.4 ml/min within 24 min. These results are consistent with the occurrence of acute renal failure in mountain climbers after free suspension on the rope even after long periods.