The reticuloendothelial system plays an important role in the prevention of bacterial infection in patients with cirrhosis. Few data are available, however, on its activity in such patients. The aim of this study was to evaluate the maximum removal capacity of hepatic reticuloendothelial system in patients with cirrhosis on the basis of study of the removal kinetics of increasing amounts of ssmTc millimicrospheres and to verie its value as a prognostic factor for death and development of spontaneous bacterial peritonitis. Common clinical and biochemical parameters, Pugh score, maximum removal capacity, aminopyrine metabolic capacity and galactose elimination capacity were measured in 43 patients with cirrhosis (33 with alcoholic cirrhosis, 8 with posthepatitic cirrhosis and 2 with cryptogenic Cirrhosis). Hepatic plasma flow and indocyanine green plasma clearance were also measured in 16 of these patients. Reference range of maximum removal capacity was determined in seven normal subjects. Maximal removal capacity below the normal range was found in 24 patients (56%). In the whole series maximum removal capacity averaged 16 2 12 pg/kg body wt/min (mean f S.D.). Maximal removal capacity was significantly correlated with serum albumin, prothrombin index, Pugh score, aminopyrine breath test, galactose elimination capacity and indocyanine green plasma clearance but not with hepatic plasma flow. During follow-up of up to 48 mo, spontaneous bacterial peritonitis developed in six patients, all with impaired maximum uptake capacity, and ll patients died. Survival was significantly shorter in patients with impaired maximum removal capacity than in those with normal maximum removal capacity (log-rank test: p = 0.024). Moreover, impaired maximum removal capacity was associated with increased risk of spontaneous bacterial peritonitis (logrank test: p = 0.037); it was also found to be an independent prognostic factor when total ascitic fluid