The induction of cytochrome P450(BM-3) in Bacillus megaterium was investigated in culture medium containing long-chain fatty acids and sodium dodecyl sulfate (SDS). Western blot analysis showed that the addition of 1 mM sodium palmitate to the culture medium resulted in 10-fold more induction of P450(BM-3) than that of 1 mM palmitic acid. There was a time lag of several hours before induction of P4508(BM-3) by sodium palmitate occurred. After the P450(BM-3) level reached a maximum value, it remained relatively constant for the rest of the stationary phase tested. SDS at 100 mu M caused a comparable effect on induction of P450(BM-3) compared with 1 mM sodium palmitate, In contrast, induction by SDS occurred relatively fast, After reaching a maximum value, the P450(BM-3) level dropped relatively fast to a very low value, Significant induction of chloramphenicol acetyltransferase (CAT) activity by sodium palmitate and SDS in B. megaterium transformed with a bm3R1-cat transcriptional fusion vector suggests that induction of P450(BM-3) by long-chain fatty acids and SDS occurs at the transcriptional level.