A minimum acceptable volume of blood for the simultaneous determination of the lipid and chlorinated hydrocarbon content was established at 50 ml. At that volume the coefficients of variation for lipid and chlorinated hydrocarbon residue determinations were > 10 and 20% respectively. Comparing chlorinated hydrocarbon levels in whole blood with serum and plasma from the same blood pool, indicated that approximately 25% of the tri-to penta chlorobiphenyls were found in the serum and 40% in the plasma. In contrast, 55–83% of the hexa-to octachlorobiphenyls were found in the serum and plasma. From among the organochlorine pesticides, between 80–110% of the trans-nonachlor and DDTs appeared in the serum and plasma, but for others this range was considerably lower (40–71%). In general no appreciable differences were observed in the recoveries of some chlorinated hydrocarbons from fortified blood and serum.