We examined the effect of a choline-devoid (CD) diet on the development of gamma-glutamyltranspeptidase (GGT)-positive foci in both sexes of the inbred rat strains Fischer 344 and PVG/R8. Following partial hepatectomy, 7 to 8 week old animals were given a choline-supplemented diet for 1 week. Two groups were then formed: one remained on choline-supplemented diet as control, and the other was switched to the CD diet. The animals were killed 10, 16 and 24 weeks later. Liver samples were then stained with hematoxylin-eosin and Masson's trichromic, and histochemically analyzed for GGT. Fatty degeneration and collagen formation was severe in F344 males while it was mild or absent in F344 females and in both sexes of PVG rats. Stereochemical quantitation showed that F344 males had a significantly greater increase in the number of positive liver foci (as well as in their mean volume and the percentage of liver occupied by them) than F344 females and PVG animals of either sex (P < 0.01). These results suggest that not only sex but also the genotype of the host plays a role in the different responses to a CD diet. In depth analysis of these factors should prove valuable to investigate this dietary model of hepatocarcinogenesis further.