Initiation activities of endogenously formed N-nitrosobis(2-hydroxypropyl)amine (NBHPA), N-nitrosodiethanolamine (NDELA) and N-nitroso-2,6-dimethylmorpholine (NDMM) were investigated in a modified short-term assay for rat hepatocarcinogenesis. Male Wistar rats were fed 1% bis(2-hydroxypropyl)amine, 0.5% diethanolamine or 0.25% 2,6-dimethylmorpholine in the diet plus 0.3% sodium nitrite in the drinking water. Two weeks after starting the experimental regimen they underwent 2/3 partial hepatectomy and were then maintained on the respective diets for a further week. Following a 2 week recovery period on basal diet rats were subjected to a resistant hepatocyte regimen consisting of 0.02% 2-acetylaminofluorene in the diet for 2 weeks and 1 mg carbon tetrachloride/kg body wt by gavage at the midpoint. Initiation activity was assayed by measuring hepatic foci positive for gamma-glutamyltranspeptidase. Numbers of such foci per cm2 were significantly increased in the groups given the secondary amines together with nitrite compared with values for groups given each precursor or nitrite alone. Further, the numbers of lesions were essentially similar to those found in rats given carcinogenic doses of NBHPA, NDELA and NDMM. The results clearly of demonstrate hepatocyte initiation activities of endogenously formed carcinogens, presumably NBHPA, NDELA and NDMM.