The interactions of alkyllead salts with avian eggs were studied bothin vitroandin vivo. During 74 h incubation in viable American kestrel (Sturnus vulgaris)eggs, trialkyl and dialkylleads (each at 50 ppb as Pb) rapidly traversed biological membranes within the eggs and were accumulated in the yolk and in the developing embryo. Since the chick resorbs the yolk just prior to hatching, it will be burdened with the majority of alkylleads present in the egg. During the experiment dialkylleads but not the trialkyllead homologs were extensively degraded.