The primary objective of this research project was to study the role of sex steroids in the pathogenesis of cholelithiasis using the Syrian hamster as a model. In addition to the morphological examination of the gallbladder epithelium, we thought it imperative to observe the changes induced in the biliary tract in response to the sex steroid treatment. This report focuses on the morphological changes induced in the liver. The hamsters were randomly divided into 4 groups, control (C), estrogen-treated (E), estrogen and medroxyprogesterone-treated (E+MP), and medroxyprogesterone-treated (MP) groups. The E group hepatocytes demonstrated proliferation of the smooth endoplasmic reticulum, lipofuscin-like granules, aggregates of glycogen rosettes, and dense bodies. Lipid droplets in the hepatocyte cytoplasm as well as the nuclei were detected in this group. E+MP combined treatment induced an exacerbation of all the changes observed in the E group, furthermore, there appeared to be a disruption of the hepatic parenchymal architecture. The MP-treated group also exhibited the architectural changes observed in the E+MP group, but also showed sinusoidal dilation. In response to MP alone, the fatty changes in the liver appeared to be accentuated. A striking feature induced in response to MP treatment, was a focal area suggestive of adenomatous changes.