The effect of the argemone alkaloid, sanguinarine, was studied on the active transport of D-glucose and some of the L-amino acids in everted sacs of the small intestine of rats. Sanguinarine (1.0 mumole) was found to inhibit (61%) the transport of D-glucose, while an alkaloid concentration of 0.1 mumole was ineffective. Both 0.1 and 1.0 mumole of sanguinarine had no effect on the transport of the L-amino acids including aspartic acid, lysine, and tyrosine. Sanguinarine showed a dose dependent inhibition of intestinal and hepatic Na+,K(+)-ATPase in a non-competitive manner. The inhibition of Na+,K(+)-ATPase by sanguinarine may in turn inhibit the active transport of D-glucose which requires a sodium pump.