Ten Staphylococcus intermedius isolates from cases of canine pyoderma and 10 from healthy carriers were examined by SDS-PAGE of exoproteins, immunoblotting and restriction endonuclease digest analysis. Similarities between banding patterns of the isolates were calculated as Dice coefficients for all three methods. For SDS-PAGE and immunoblotting, no significant differentiation was found between the pyoderma and "healthy" groups. Analysis of DNA digested with BglII indicated that S. intermedius is genetically heterogeneous; Dice coefficients for the pyoderma group were distinct from those for the healthy group (p < 0.001), and cluster analysis confirmed that the pyoderma isolates (9) formed a group separate from the majority (6 of 9) of the normal isolates.