Both the simple hexane extraction and the heat volatization method give good recovery of chlorinated hydrocarbon insecticides from water. In vitro binding of all these materials can be demonstrated by both analytical methods. This suggests the possibility of binding in vivo, but it is certain that the two kinds of binding are not identical. The volatilization method gives lower recovery of added material, but it gives higher recovery of the same materials present through metabolism in blood taken from the general population. Application of the volatilization method demonstrated higher concentrations of pesticides and their metabolites in the plasma of men as compared with the plasma of women, and the same was true in some instances of whole blood and RBC.