The metabolic and kinetic behaviour of different garlic (Allium sativum L., Alliaceae) constituents were investigated in the isolated perfused rat liver, using aqueous extracts of garlic powder as well as isolated allicin, the main product of the enzymatic degradation of alliin. Allicin (allyl thiosulfinate) showed a remarkable first pass effect and passed the liver unmetabolized only at high concentrations which caused considerable cell injuries. Diallyl disulfide and allyl mercaptan were identified as metabolites of allicin, whereby diallyl disulfide probably is the metabolic precursor of allyl mercaptan as shown by perfusion with diallyl disulfide alone. The metabolites diallyl disulfide and allyl mercaptan could be determined in the perfusion medium as well as in the bile and the liver tissue. Other degradation products of garlic were also investigated in this model. Ajoenes and vinyldithiins were detected in perfusion medium after liver passage but no metabolites of them could be identified up to now.