Four groups of 80 ICR SPF mice of each sex were fed 0-12.5 ppm technical chlordane for 104 weeks. Male and female mice were examined for hematological, biochemical, urinary, and pathological changes at 52 and 104 weeks of exposure. Serum AST (= SGOT) and ALT (= SGPT) were elevated in treated males and females, liver weights were increased in the 12.5-ppm groups, and masses were seen in the livers of 12.5-ppm males. Increased liver cell volume was seen in 5- and 12.5-ppm males and females, while hepatocyte degeneration and necrosis were seen only in treated males. Hepatic hemangiomas and hepatocellular adenomas typically occurred together and were significantly increased in 12.5-ppm males. No other significant changes were detected. However, the incidence of tumors in the 12.5-ppm males was within the range of historical controls. Accordingly, there was no evidence that chlordane induced tumors in the ICR mice. A long-term no-observed-effect level (NOEL) of 1 ppm chlordane in the diet was found.