The ability of antimony and antimony containing parasiticidal agents to enhance the rate of heme degradation in liver and kidney was investigated. Trivalent antimony was shown to be an extremely potent inducer of heme oxygenase, the initial and rate limiting enzyme in heme degradation, in both organs, whereas pentavalent antimony was a weak inducer of this enzyme. The ability of antimony to induce heme oxygenase was dose dependent, independent of the salt used, and not a result of a direct activation of the enzyme in vitro. Concomitant with heme oxygenase induction by antimony, microsomal heme and cytochrome p450 contents decreased. /Trivalent, pentavalent, antimony containing parasitical agent/