Previous studies (Parizek et al., 1969) have shown significant interactions between selenium and certain heavy metals, particularly mercury and cadmium. Since these elements have an affinity for sulfhydryl groups, it was proposed that a similar interaction might exist with lead. In an initial experiment, adult quail hens were given diets supplemented with 0 and 1 p.p.m. selenium and 0, 500 and 1000 p.p.m. lead in a 2 X 3 factorial arrangement. After 32 days of feeding, body weight, liver weight and egg production decreased in birds fed lead while kidney weights increased. Highly significant decreases in red blood cell delta-aminolevulinic acid dehydratase (RBC-ALAD) activity occurred when lead was added to the diet. Control RBC-ALAD activity was 1337 versus 105, 91, 156 and 110 nmol. porphobilogen produced per ml. of erythrocyte per hour (nmol. PBG/ml. RBC/hr.) for the 500, 1000, 500 plus selenium and 1000 plus groups, respectively. After 85 days of feeding lead to male birds in a second study, selenium appeared to have variable effects on the concentration of lead in liver, kidney and tibia. Selenium supplementation to lead diets resulted in significantly increased levels of lead in kidney tissue while little or no effects were observed on liver or tibia lead levels. RBC-ALAD activity was significantly reduced with lead supplementation and no effect of selenium addition was observed. Electrophoretic gels of serum from birds fed lead containing diets showed increased protein bands in the transferrin and globulin regions regardless of the presence of 1 p.p.m. selenium. A third study was conducted to determine the effects of supplementing an isolated soy protein diet with 0 and 1 p.p.m. selenium and 0 and 3000 p.p.m. lead. Selenium supplementation improved body weights over controls while lead additions caused reduced egg production and ALAD activity. Lead feeding increased tibia/body weight ratios and lead concentrations in liver, kidney and tibia. No significant interaction between lead and selenium was observed.