A selected fraction of non-parenchymal cells was prepared from the liver of untreated rats, of rats 11-13 days after ligation of the common bile duct, and of rats fed for 4-5 weeks a choline devoid diet containing DL-ethionine. The cell fraction isolated from these livers consisted of one type of mesenchymal cells (Kupffer cells), and of increasing proportions of gamma-glutamyltranspeptidase-positive non-parenchymal epithelial cells (bile ductule/oval cells). The activities of aminopyrine N-demethylase and of aniline hydroxylase were determined in the three cell fractions, and were found to be less than 10% of the same enzyme activities of purified hepatocytes isolated from untreated rats. Primary cultures of untreated rat hepatocytes, and of the non-parenchymal cell fraction prepared from the liver of untreated and treated rats, were exposed to aflatoxin B1. Less than 0.5% of the hepatocytes from untreated rats survived a 48 h exposure to a concentration of 10 to the minus 6th power M aflatoxin B1. On the other hand, 75% or more of the non-parenchymal cells survived a 48 h exposure to a concentration of aflatoxin B1/cell two and a half times as great. (Copyright (c) International Union Against Cancer, 1983.)