Experiments were undertaken to study, in vitro and in vivo, the metabolism or highly chlorinated. naphthalenes by the albino rat and the calf. Three studies were made. The first involved the determination of the amount of uptake of hexaehloronaphthalene by rat liver and kidney tissue. Similar studies on calf liver and kidney also were made. Secondly, balance studies were conducted, comparing the relative amounts of hexa- and octachloronaphthalene absorbed after feeding these compounds to rats. Finally, experiments were undertaken to investigate the possible formation of conjugated products as a means of chlorinated naphthalene metabolism. From the studies, a number of conclusions were derived. 1. In the rat and calf, liver seems to be an active metabolizing or detoxifying organ as evidenced by uptake of hexachloronaphthalene by liver of both these animals. Kidney on the other hand showed no uptake in either animal. Calf liver has a greater capacity tor hexachloronaphthalene uptake than does rat liver tissue. / Master of Science