Reversed-phase high Performance liquid chromatography (C18-HPLC) was used to separate and quantitate all the detectable alkyl and alkenyl thiosulfinates, including configurational isomers, of garlic homogenates. Pure thiosulfinates were synthesized or isolated and identified by 1H-NMR, and their extinction coefficients determined. Some configurational isomers required Separation by silica-HPLC. Five previously unreported thiosulfinates have been found, four of which contain the trans-1-propenyl group and increase several-fold to over half the content of allicin upon storage of garlic bulbs at 4°C with a concomitant decrease in a γ-glutamyl peptide. The variation in thiosulfinate yield between different countries, stores, bulbs, cloves, and storage times was investigated. A method for standardizing the quantitation of allicin yield from garlic is proposed and compared to other methods of allicin analysis.