Leukotriene C4 binding to mouse brain membranes was readily displaced by S-alkylglutathione derivatives, with the affinity of the test compound increasing as the alkyl chain length increases. S-decylglutathione was as potent as leukotriene C4. These data suggest that brain membrane leukotriene C4 binding sites are S-alkylglutathione binding sites, possibly microsomal glutathione transferase.