Effect of vitamin A compounds on the covalent binding of benzo(a)pyrene [B(a)P] to subnuclear components was studied using rat liver nuclei in vitro. The retinol-induced inhibition of the covalent binding of B(a)P depended both on the dose and the time of addition. Retinal and retinyl acetate were both potent inhibitors, but retinoic acid was less effective. Retinol induced marked inhibition of B(a)P binding to DNA and protein of the nuclear matrix but had little or no effect on the labeling of bulk DNA and protein in chromatin fractions.