Alamethicin affects glucuronidation of phenolic substrates. Different alamethicin concentrations lead to different depletion rates. A maximal glucuronidation activity could be assigned to different but distinct alamethicin concentrations. Alamethicin application is a crucial factor to deduce enzyme kinetic parameter from in vitro metabolic assays. Correlations between the substrate lipophilicity and alamethicin effect were not detected.