Four pharmacons were tested on an acute portal pressure lowering effect in an experimental animal model with 25 normal and 25 rats with Thioacetamide-toxic liver cirrhosis. Invasive measurements of arterial and portal pressure were made under Hexobarbital-Sodium anaesthesia during 30 minutes after pharmacon application. The portal pressure of cirrhotic rats was under basic conditions 9.5 +/- 1.5 mm Hg and significant higher as in normal animals (5.3 +/- 0.9 mm Hg, p less than 0.01). After 10 mg/kg body mass Propranolol the portal pressure decreased in both animal groups small but not significantly over the whole measurement time. 1 mg/kg Verapamil lowered arterial middle pressure significantly, but increased portal pressure at all 15-20% in both animal groups. Application of 0.1 mg/kg Prazosin decreased the arterial middle pressure at all 5-15% and the portal pressure at all 20-30% in both study groups (both significantly). For Canrenoat-Potassium (20 mg/kg) no clear effect could by evaluated on portal pressure. The model of Thioacetamide-toxic cirrhosis of the rat offers conditions like cirrhosis in human medicine in order to study the effects of portal pressure lowering pharmacons. Propranolol and Prazosin decrease portal pressure and should by further investigated.