American kestrels (Falco sparverius) were fed diets containing 3 ?g/g Aroclor?l 1248 or control diets from mid-January until July. Eggs were removed from first clutches 2 to 4 days after laying ceased and shell thickness and shell dimensions were measured. Contents of the third egg of each clutch, the carcasses of all adults that received Aroclor? 1248 and of three males and three females that received the control diet were analyzed for DDE, Aroclors? 1248, 1254 and 1260, and dieldrin. Concentrations of PCBs, DDE and dieldrin were significantly higher (P < 0.03) in eggs and carcasses from treated adults than in controls. Shell thickness and shell thickness index of eggs from treated adults were reduced 5.0% (P < 0.0001) and 4.8% (P < 0.0001), respectively, from those of controls.