Modulatory influence of Andrographis paniculata crude extract on cytochrome P450 (CYP) enzymes was performed by administration of the crude extract of Andrographis paniculata to ICR male mice. Total hepatic P450 content was not significantly modified by either the aqueous or the alcoholic extracts of Andrographis paniculata. Assessment of hepatic microsomal P450 activities by alkoxyresorufin O-dealkylations noted that both the aqueous and alcoholic extracts of Andrographis paniculata significantly increased ethoxyresorufin O-dealkylase and pentoxyresorufin O-dealkylase activities, while those of methoxyresorufin O-dealkylase activities were not elevated. These results suggested that Andrographis paniculata might effectuate hepatic cytochrome P450 enzymes of which CYP1A1 and CYP2B are the responsive P450 isoforms.