The effects of iron and salicylate on the expression of cytochrome P450s in Bacillus megaterium were investigated in this report. Immunoblot analysis showed that the addition of 4 mM ferric iron or 10 mM salicylate to the culture medium resulted in a significant increase in the P450(BM-1) level, while the same condition had Little effect on P450(BM-3) expression. Substantial induction of chlorampheni col acetyltransferase (CAT) activity by iron and salicylate in B. megaterium cells bearing a P450(BM-1) promoter-car transcriptional fusion vector suggests that the induction of P450(BM-1) by iron and salicylate occurs at the transcriptional level. Unexpectedly, in contrast to the bm1P1-dependent induction of P450(BM-1) by pentobarbital, disruption of bm1P1 gene did not affect induction of P450(BM-1)., by iron and salicylate. This result suggests that the induction of P450(BM-1) by iron and salicylate occurs by a bm1P1-independent mechanism, To our knowledge. this is the first example of an iron-regulated cytochrome P450 gene in prokaryotes.