A dose related carcinogenic response was established for dimethylm'trosamine administered in the diet of rainbow trout (Salmo gairdneri). An equation was derived for the relationship between dose and hepatocellular carcinoma incidence. From a published dose response study using Porton rats as a test animal, a second equation was derived for comparison. The rat and the trout were approximately equivalent in their sensitivity to dimethylnitrosamine carcinogenesis. The histological nature of the

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... rcinogenic response in trout was similar to to that of mammalian species. Apart from carcinogenesis, no indications of chronic toxicity were observed after a one year feeding experiment. The median lethal dose after intraperitoneal injection of dimethylnitrosamine was 1,770 mg/kg body weight in rainbow trout. Relative to the range of 15 to 50 mg/kg body weight reported for several mammalian species, trout were resistant to the acutely toxic effects of dimethylnitrosamine. ACKNOWLEDGEMENTS I wish to thank Dr. R. A. Scanlan and Professor R. 0. Sinnhuber for their guidance during this investigation. Additional thanks are owed to the other members of my graduate committee and to the faculty, staff and students of the Food Science and Technology Department for their interest and cooperation. I wish to acknowledge the assistance of Dr. D. Pierce in the statistical evaluation of this study. A special thanks is extended to Dr. J. Hendricks and Mrs. L. J. Hunter for their contribution to the histology portion of this study. The assistance of the entire staff of the Food Toxicology and Nutrition Laboratory is gratefully acknowledged. Thanks are also due to Gregory M. Grieco for his indulgence throughout this study.