Oxidation of 1-octene by cytochrome P-450 results concurrently in formation of 1,2-oxidooctane and in N-alkylation by the catalytically activated olefin of the prosthetic heme group. The stereochemistry of trans-1-[1-2H]octene is retained during both transformations. This alkylation stereochemistry requires addition of the pyrrole nitrogen and the activated oxygen to the same side of the double bond, a reaction geometry opposite to that expected if the heme were alkylated by the epoxide metabolite. Stereochemical analysis shows that the S enantiomer of the epoxide is formed in slight excess over the R enantiomer by oxidation of the re and si faces, respectively, of the olefin, but that heme alkylation only occurs during oxidation of the re face. The stereochemical specificity of epoxidation and heme alkylation requires that (a) the two processes proceed by independent (probably concerted) mechanisms, or (b) the two processes diverge from a common acyclic intermediate.