Regulation of induction of P450IA1 (P-450E) in teleosts was examined by investigating temporal relationships between P450E protein, activity, and mRNA levels, and measuring protein and heme turnover, in the teleost Fundulus heteroclitus. Monoclonal antibodies used for P450E protein detection were specific in immunoblots for purified scup (Stenotomus chrysops) P450E, a single band corresponding to P450E in scup microsomal mixtures, and the xenobiotic-inducible orthologue in other fish including Fundulus. P450E mRNA was measured by translation of total RNA, precipitation with anti-P450E polyclonal antibodies and autoradiography, or by hybridization of RNA with a trout P450IA1 cDNA. P450E and ethoxyresorufin O-deethylase activity rose coordinately after treatment with Beta-naphthoflavone, lagging behind mRNA increases by about 25 hours. mRNA levels declined rapidly, despite prolonged elevated protein and activity levels. In a dual label experiment, P450E was precipitated from solubilized microsomes. The apoprotein was calculated to have a half-life of 32 to 43 hours, the heme moiety a longer half-life of 104 hours. These results support a hypothesis that transcriptional enhancement is involved in initial stages of P450E induction, while other forms of control are important in maintenance of P-450E expression. This study addressed a specific chemico-biological interaction-- the organism's biochemical response to a challenge by foreign compounds--which occurs in the marine environment. Xenobiotic metabolism, Enzyme induction, Cytochrome P-450.