1,2-Dithiole derivatives of the formula: ##STR1## wherein Het represents a pyridazin-3-yl radical, or a pyrimidin-2-yl, -4-yl or -5-yl radical, each such radical being optionally substituted by a halogen atom or by an alkyl radical of 1 through 4 carbon atoms, an alkoxy radical of 1 through 4 carbon atoms, the mercapto radical, an alkylthio radical of 1 through 4 carbon atoms or a dialkylamino group having 1 through 4 carbon atoms in each alkyl radical, are new compounds useful in the treatment of bilharziasis and amoebiases.