The colloidal characteristics of a biotechnologically produced hydrophilic sulphur suspension have been compared to those of a synthetically formed LaMer sulphur sol. Biologically produced sulphur is the end-product of microbiological sulphide oxidation, a process carried out by mixed cultures of Thiobacillus-like bacteria.Electrophoretic mobility measurements and flocculation experiments revealed differences in the colloidal properties of the two sols. This observation was explained by the assumption that negatively charged (bio)polymers are attached to the microbiologically produced sulphur particles, which have an orthorhombic sulphur nucleus, while a LaMer sol has a vesicle structure which is built up of long-chain polythionates.As shown by dynamic light scattering measurements, the diameter of the biological sulphur particles decreases with increasing salt concentration, indicative of an inward shift of the adsorbed polymers at high electrolyte concentrations.