Body weight gain and hepatic concentrations of vitamin A were reduced in Sprague‐Dawley rats by pre‐ and postnatal exposure to 100 ppm polybrominated biphenyls (PBBs). The ratio of liver weight to body weight, activity of hepatic δ‐aminolevulinic acid (ALA) synthetase, and urinary excretion of uro‐ and coproporphyrins were increased by PBBs. Treatment with PBBs also increased the left atrial inotropic response to calcium. However, PBBs had no effect on development of the adrenergic neuronal transport system in heart, left atrial baselike peak tension, or inotropic response to ouabain. Thus PBBs retarded body weight gain and produced a variety of alterations in liver, but had little effect on cardiac contractile function.