Carbon tetrachloride (CCl4) was intraperitoneally injected into Balb/c mice 4 times at biweekly intervals, and the morphological changes of the liver and kidney were examined during 12 weeks after the last injection. The renal injuries progressed in spite of cessation of CCl4 treatment; microcysts with tubular-cell degeneration were manifest on day 42 after the last injection of CCl4. At the end of the experiment, however, interstitial fibrosis with inflammatory cell infiltration was much more prominent. Glomerular changes with IgG deposits also developed following the tubulointerstitial changes. The CCl4 treatment induced liver damage as well, but it promptly subsided without formation of cirrhosis. The CCl4 nephrotoxicity was completely inhibited by whole body irradiation (200 rad) exposed at each injection of CCl4. In contrast, the hepatic damage was not changed by irradiation. These results seem to indicate etiologic independence of renal and hepatic events induced by CCl4 treatment. It is also suggested that chronic CCl4 nephrotoxicity is mediated, at least in part, by radiosensitive responses of the mice themselves.