The cell-surface charge and cell-surface hydrophobicity of 10 strains of Azospirillum spp. were evaluated by the aqueous, two-polymer phase partitioning assay. Azospirillum spp. had moderate cell-surface hydrophobicity and charge, lower than known values for human pathogens. The hydrophobicity and charge values were higher in solid than in liquid media. A general pattern of modifying hydrophobicity and charge by external treatments of the cells of all strains was not found, but various chemicals, temperatures, and enzymatic treatments changed the cell-surface hydrophobicity and charge in different strains. A similar hydrophobic protein was isolated, and partially characterized, from two strains of A. brasilense and one strain of A. lipoferum. This study proposes: (i) cell-surface hydrophobicity and charge of Azospirillum spp. can be affected by external treatments of the bacterium cell, and (ii) hydrophobicity and charge may play a role, perhaps small, in the primary adsorption of Azospirillum spp. to surfaces.