This study was aimed at investigating whether portal pressure, which is usually measured in the morning, is subject to circadian variations in patients with cirrhosis. Furthermore, a possible circadian variation for the occurrence of variceal bleeding was also investigated. Ten patients with alcoholic cirrhosis and portal hypertension had serial measurements of portal pressure, evaluated by the hepatic venous pressure gradient (the difference between wedged and free hepatic venous pressures), during a 24-hr period. In addition, a survey of the hour of occurrence of variceal hemorrhage was performed in 101 consecutive cirrhotic patients with hematemesis, in whom the precise moment of onset of bleeding could be determined, and the origin of bleeding was confirmed by emergency endoscopy. Statistical evaluation with the population-mean cosinor method allowed detection of a circadian variation in portal pressure. Portal pressure progressively declined during the afternoon and evening (from 17.9 +/- 5.3 mm Hg at 12 PM to a nadir of 16.8 +/- 4.9 mm Hg at 7 PM (p < 0.05). Thereafter, portal pressure increased during the night, returning to baseline values at 9 AM (18.1 +/- 5.1 mm Hg). The acrophase was at 8:32 AM (+/- 100 min) with an amplitude of 3.45 +/- 1.1 (% of mean +/- S.E.) (rhythm detection: p < 0.03). Similarly, the analysis of the time of occurrence of variceal hemorrhage with the use of a multiple-components rhythmometry test disclosed two peaks in the prevalence of esophageal bleeding.(ABSTRACT TRUNCATED AT 250 WORDS)