In 10 healthy men aged 25 to 35 years the variability of basal arterial blood flow (BBF), maximal arterial blood flow (MBF) as induced by a 5-minute arterial occlusion, total venous capacity (TVC) and venous emptying rate (VER) were studied in both the upper and lower limbs by repeated measurements over 5 hours under strictly standardised conditions using an automatic venous occlusion plethysmograph. Mean values obtained at the initial examination in the forearm and calf respectively were: BBF: 3.7 +/- 1.2 and 2.3 +/- 0.6, MBF: 24.2 +/- 6.5 and 28.0 +/- 8.9, VER: 64.0 +/- 14.0 and 66.0 +/- 16.4 ml/min per 100 g tissue, TVC: 3.5 +/- 0.9 and 3.7 +/- 0.8 ml per 100 g tissue. At 45 min there was a general trend towards lower values in particular regarding BBF and TVC. Reproducibility in terms of coefficients of variation computed from duplicate determinations were 25% and 13% for BBF and 11% and 7% for MBF measurement in the forearm and calf respectively and below 10% for TVC and VER. The low reproducibility of BBF measurement is apparently due to a high degree of random biological variability in particular concerning the forearm vascular bed which makes the forearm poorly suitable for studying effects of interventions in cardiovascular control.