SDS-PAGE fingerprinting of cell-wall proteins extracted from 119 strains belonging to different species of lactic acid bacteria have been compared. The method of extraction and electrophoretic separation utilized in this work was found to be a reliable and rapid way for characterizing thermophilic lactobacilli species and strains. A protein of approximately 50 kDa was found to be characteristic for all the Lact. helveticus strains, and two cell-wall proteins of about 20 and 30 kDa were typical of the species Lact. delbrueckii, but the discrimination between the subspecies lactis and bulgaricus was not possible by the electrophoretic technique used. The other thermophilic species studied in this work presented cell-wall protein patterns that permitted their differentiation from both Lact. helveticus and Lact. delbrueckii.