Alcoholic extracts of the heartwood of Liriodendron tulipifera have demonstrated antimicrobial activity against Staphylococcus aureus, Mycobacterium smegmatis, Candida albicans, and Aspergillus niger. The antimicrobial activity was associated only with the alkaloidal fraction. Separation of the active alkaloidal fraction by chromatography led to the isolation and identification of dehydroglaucine and liriodenine as the active components. Several other alkaloidal derivatives were prepared and tested. In addition to the active alkaloids, michelalbine was also identified in the tertiary nonphenolic base fraction along with the lignan, lirioresinol-B-dimethyl ether, and two N-acetylnoraporphine alkaloids from the nonbasic fraction.