An infrared study has been carried out on 2-mercaptobenzothiazole and two of its derivatives (6-methyl-2-mercaptobenzothiazole and 6-methoxy-2-mercaptobenzothiazole) adsorbed on the PbS (galena) surface from aqueous solution. Different molecular structures were tested in order to observe the influence of the ring substituents on the surface interaction. The Pb bulk complexes of the studied molecules and the PbS surface treated in their aqueous solutions have been compared. The difference in adsorption on PbS was studied by varying the concentration of the reagents.