title: Bioassay of dieldrin for possible carcinogenicity.
abstract: A bioassay of purified technical-grade dieldrin for possible carcinogenicity was conducted by administering the test chemical in feed to Fischer 344 rats. Groups of 24 rats of each sex were administered dieldrin at one of three doses, either 2, 10, or 50 ppm, for 104-105 weeks. Matched controls consisted of groups of 24 untreated rats of each sex. All surviving rats were killed at 104-105 weeks. Body weights of the rats were essentially unaffected by the treatment, but typical signs of organochlorine intoxication including hyperexcitability, tremors, and coma were observed in high-dose males beginning in week 76 and in high-dose females beginning in week 80. Survival was not adversely affected, and adequate numbers of rats were available for meaningful statistical analyses of the incidences of tumors. A variety of neoplasms occurred in control and treated rats; however, the incidences were not related to treatment. It is concluded that under the conditions of this bioassay, dieldrin was not carcinogenic in Fischer 344 rats.