Phage type 29 Staphylococcus aureus was identified singly or with type 52 in 64.1% of 248 coded isolates from patients with toxic shock syndrome. These phage types also have a high capability of producing pyrogenic exotoxin C and enterotoxin F. The origin and development of these toxigenic strains were explored by studying 25,220 isolates of S. aureus stored in a staphylococcal bank between 1960 and 1979. A small percentage of phage types 29, 52 were found in 1960, but their prevalence increased between 1961 and 1970, and continued at elevated levels through 1979. The toxigenic capabilities of these phage types were apparently acquired about 1971 and increased up to 1975. High levels of prevalence persisted during the following 4 years, and receded in 1980 and 1981. Other evidence during 1980 and 1981 indicates that these strains of S. aureus have become an important pathogen in surgical wounds, burns, and other infections.