Bacteriophages were released by 98% of 100 Staphylococcus hyicus strains studied after treatment with mitomycin C. Twenty-three phages with different lytic spectra were included in a phage typing system and used for typing S. hyicus. On a test-set of 100 epidemiologically unrelated S. hyicus strains isolated from Danish pig herds, the phages were able to type 92% of the strains, producing 16 different phage types. Reproducibility of the phage typing system after subculture of the strains and using fresh phage stock was 96%. Typability ranged from 52 to 80% when typing porcine strains originating from other countries. Although phages were isolated from porcine skin strains exclusively, the system produced phage types in S. hyicus strains of bovine origin. Ten strains of S. aureus and S. chromogens were not typable by these phages. Strains belonging to one phage type (A/B/C/W) were isolated significantly more often from piglets with exudative epidermidis than from healthy piglets. The phage typing system described appears to be a valuable tool in diagnosis of exudative epidermidis in pigs, and furthermore, might be of value in epidemiological studies of S. hyicus.