Over the last 50 years, many species of amphibians have declined markedly, and even become extinct throughout the world. The cause of this is not clear, and several factors may be involved, including exposure to contaminants. The effects of some pollutants (i.e., chromium and heptachlor epoxide) on the green frog (.Rana kl. esculenta) were assessed experimentally, using morpho‐histological techniques. At the lowest doses used (0.5 ppm for Cr, 4 ppb ‐ 40 ppb for heptachlor epoxide), the hepatocytes showed no relevant structural or functional changes. The highest dose (5 ppm for chromium and 400 ppb for heptachlor epoxide) proved to affect the hepatocytes, as revealed mainly by intense ROS reactivity and by increased SDH activity. In addition, relevant variations in melanin content and distribution, as well as in hemo‐siderin deposits, were observed in melanomacrophages. These cells also showed an intense dose‐dependent reactivity for both acid phosphatase and catalase in the liver of treated anima...