Rats submitted to p,p'-DDT at 200 ppm in drinking water showed increased p, p'-DDT storage which was not statistically different from that of thyroidectomized rats receiving p, p'-DDT. Rats receiving p, p'-DDT also showed increased fat storage of total o, p'-DDT and Dieldrin and decreased total BHC storage.Thyroidectomy decreased the amount of p, p'-DDT naturally occurring in the animal body and raised the metabolization of this compound.In thyroidectomized rats submitted to the same dosage of p, p'-DDT, increased storage of p, p'-DDT, o, p'-DDT and Dieldrin was found. A statistically significant increase in BHC was also observed.It is concluded that p, p'-DDT in the diet may affect the storage level of other organochlorine insecticides depending on its concentration, and that the physiopathological state of the body, e. g. thyroidectomy has a definite influence on the storage of organochlorine insecticides in the animal body and on their biological effect.