We examined the effect of diethylpyrocarbonate (DEPC), a histidine specific reagent, on H+ coupled transport of cephradine via dipeptide carriers in the intestinal brush-border membranes, in comparison with the effects of other chemical modifiers. Pretreatment of membrane vesicles with DEPC resulted in the inhibition of cephradine transport in the presence or absence of an inward H+ gradient. This inhibition was reversed by subsequent treatment with hydroxylamine, but not with dithiothreitol. The inactivation by DEPC pretreatment was abolished by the presence of cephradine or glycylsarcosine. In the DEPC-pretreated membranes, the V(max) value of cephradine uptake was decreased without any change in the Km value. In contrast, cephradine uptake was not changed by the pretreatment with N-acetylimidazole, a tyrosine specific reagent, or p-chloromercuribenzene sulfonate, a sulfhydryl reagent. These results suggest that histidine residues in the carriers are essential for H+ coupled transport of amiocephalosporins.