The aim of this study was to determine the physicochemical surface characteristics of seven lactobacillus strains, including L. acidophilus RC14, L. casei subsp. rhamnosus RC15 and GR1, L. acidophilus T13, L. casei subsp. rhamnosus ATCC7469, L. fermentum B54, and L. casei #36. Surface characteristics investigated comprised hydrophobicity, zeta potentials, molecular composition, elemental surface composition, and surface morphology. These characteristics were determined by water contact angle measurements, microelectrophoresis, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy on stained sectioned cells, respectively. Differences between strains with respect to water contact angles, ranging between (19^{\circ}) and (105^{\circ}), and isoelectric points, varying from 1.8 to 3.8 , could be related with compositional data obtained by XPS and FTIR. These relations indicated that the presence of (glyco-) proteinaceous material at the cell surface results in a higher hydrophobicity, whereas a hydrophilic surface was associated with the presence of polysaccharides. It is argued on the basis of these relations that XPS and FTIR (although the latter is not generally considered a surface-sensitive technique) both yield physiologically relevant information on the cell surfaces, despite the fact that these techniques require freeze-drying. 1993 Academic Press, Inc.