Monoclonal antibodies toward rabbit liver cytochrome P-450 isozyme 6 (P-450 6) were used to identify several recombinant clones from a pBR322 cDNA library that express beta-lactamase-P-450 6 hybrid proteins. The nucleic acid sequence and predicted amino acid sequence of a rabbit P-450 6 cDNA shows a high degree of homology with rat P-450c and mouse P1-450. When used as a probe to rescreen the library, the P-450 6 cDNA hybridized to several heterologous classes of cDNAs. One such class was shown to encode P-450 4 by comparison of its predicted amino acid sequence to amino acid sequences of cysteine-containing tryptic peptides derived from P-450 4. DNA sequence analysis of a cDNA clone belonging to a third class demonstrated that it contained a 131-base-pair intervening sequencing when compared to the cDNA coding for P-450 6. This sequence corresponds in location to intron E of the rat P-450c gene. Blot-hybridization analysis demonstrated that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) dramatically induced P-450 4 and 6 mRNAs, which differ in size. The sizes of these mRNAs differ from their analogs in the mouse as a result of divergence in the 3' untranslated portions of the mRNAs.