Estimation of Michaelis--Menten constants in microsomal enzyme systems by the direct linear plot and least squares regression.

1. Data from in vitro liver microsomal metabolism of ethylmorphine aniline and benzpyrene in male rats and male and female quokkas (Setonix Brachyurus) were fitted to the Michaelis--Menten equation by Wilkinson's non-linear regression procedure and Eisenthal and Cornish-Bowden's direct linear plot. 2. Ethylmorphine and aniline metabolism in the male quokka were non-ideal, but in all other instances there were no differences in the performance of the two methods.