By using fluorescent probes the distribution and fluid properties of lipid and saccharide-bound molecules was assessed in the tegument of praziquantel (−) treated Schistosoma mansoni adult male worms. Our results show that higher amounts of glycoproteins and/or glycolipids are exposed in damaged areas of the membrane compared with undamaged ones. At damaged regions these molecules present high lateral diffusion coefficient and mobile fraction values which suggests that after praziquantel(−) treatment they are being shed by the worm into the medium. The lateral diffusion coefficient of the lipid analogue 5'-octadecanoyl aminofluorescein is unchanged in damaged or undamaged areas but the mobile fraction is significantly reduced at damaged areas. The immunological significance of these altered surface properties is discussed.