Corynebacterium diphtheriae strains expressed variation in hydrophobic characteristics dependent on the method used. Results of single assays are not a reliable representation of C. diphtheriae hydrophobicity. All 12 strains adhered to polystyrene surfaces; three showed spontaneous aggregation (SA) in Trypticase Soy Broth (TSB) medium, and eight exhibited autoagglutination in phosphate-buffered saline (PBS; AA-positive). The salt aggregation test (SAT) values less than or equal to 0.002 or greater than or equal to 1.6 represented breakpoints for groups of strains with differing hydrophobicity. C. diphtheriae strains showed affinity towards n-hexadecane. Percentages of adhesion varied from 31% to 63% and were not directly related to morphological n-hexadecane adhesion patterns. Diffuse and localized adhesion patterns were noted predominantly among sucrose-positive and sucrose-negative strains, respectively. Strains of the sucrose-negative biotype expressed a higher degree of hydrophobicity. The choice of the growth medium influenced the hydrophobicity, not the hemagglutinating activity (HA) of C. diphtheriae. Heating bacterial suspensions at 121 degrees C decreased both HA and hydrophobicity of three strains. However, hydrophobins and hemagglutinins were trypsin and detergent resistant. The treatment of microorganisms with Clostridium perfringens neuraminidase increased the hydrophobicity but not the HA titers of strains tested. Hemagglutinins were partially responsible for hydrophobicity. Hydrophilic AA-negative strains adhered strongly to glass but expressed weak HA. Sialylglycoconjugates functioned as hydrophilins on C. diphtheriae surfaces.