Lindane, the gamma -isomer of hexachlorocyclohexane, one of the most widely used insecticides, was incorporated into carp food for 109 days. The effects of 10, 100, or 1000 ppm of lindane in food on hematocrits and on antibody production against Yersinia ruckeri bacterin in sera and mucus were followed for 79 days. No effect of lindane on these parameters and on spleen weight was observed. Lymphoid organs, spleen and kidney, were as highly contaminated at the beginning of the inoculation (Day 30) as at the end of the experiment. The tissue levels of lindane in liver, spleen, kidney, or whole body, determined after 30 and 109 days of contamination, indicated that the tissue distribution was dependent on organ lipid contents.