title: Bioassay of diazinon for possible carcinogenicity.
abstract: A bioassay of diazinon for possible carcinogenicity was conducted by administering the test chemical in feed to F344 rats and B6C3F1 mice. Groups of 50 rats and 50 mice of each sex were administered diazinon at one of two doses, either 400 or 800 ppm for the rats and either 100 or 200 ppm for the mice, for 103 weeks and were then observed for an additional 1 or 2 weeks. Matched controls consisted of groups of 25 untreated rats and 25 untreated mice of each sex. All surviving animals were killed at the end of 104 or 105 weeks. There was no appreciable effect of administration of diazinon on mean body weights of rats or mice of either sex. Mortality was not increased in any of the dosed groups of rats or mice, when related to that in the corresponding controls, and survival was 84% or greater in all dosed and control groups of animals at week 78. Some hyperactivity was noted in the dosed groups of both species; however, both the rats and mice may have been able to tolerate higher doses. Sufficient numbers of animals were at risk in all groups for the development of late-appearing tumors. No tumors occurred in any of the dosed groups of rats or mice of either sex at incidences that could clearly be related to the administration of diazinon. It is concluded that under the conditions of this bioassay, diazinon was not carcinogenic for F344 rats or B6C3F1 mice of either sex