SUMMARY The generally held views that plasma renin activity (PRA) is increased in cirrhosis and that this is secondary to reductions in the "effective" blood or extracellular fluid (ECF) volumes, consequent on the effects of portal hypertension, were re-examined in the present study. Measurements of PRA in 67 patients representing different clinical stages of cirrhosis showed that the mean value in 15 patients'without ascites was significantly reduced. In 21 of 35 with ascites, PRA was either reduced or within the normal range. A low plasma renin substrate concentration was not the cause for the low PRA. These findings are not in keeping with the concepts of reduced "effective" blood or ECF volumes at least for the majority of patients at these stages of cirrhosis under the conditions of the present study. The only group showing a significantly increased PRA had evidence of renal impairment. In these 17 patients the underlying reduction in renal perfusion may have been the stimulus to the kidney that led to an increase in renin secretion.