Fifty‐nine male Sprague‐Dawley rata were subjected to an end‐to‐side portacaval shunt and compared with appropriate controls. During the first ten days after the operation, the liver weights decreased from an average of 4.2 to 2.3% of the body weight and thereafter remained at this level. Testicular atrophy also occurred regularly but only after the tenth postoperative day. Three weeks after the operation, the body weight of shunted rats had decreased by an average of 20%, whereas sham operated controls gained 17%. These changes were related to food intake and coprophagy. Hyper‐ammonaemia developed gradually and levelled off at about 500 (μg/100 ml. Other alterations were more variable in severity. Spontaneous motor activity decreased to 12–77% of the preoperative value and was significantly correlated with changes in body weight. The electrocorticographic pattern was characterized by an average increase in rapid waves to 205% after five to six weeks, whereas the slow waves remained unchanged. These studies have established a standard of reference for further investigations with this animal model.

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