A total of 281 Staphylococcus aureus strains selected from those submitted to the Centers for Disease Control for phage typing between 1956 and 1982 were tested for the production of toxic-shock-associated protein (TSAP) by isoelectric focusing (IEF) and solid-phase radioimmunoassay. The results suggest that the observed temporal trends in the incidence of toxic-shock syndrome were not primarily due to changes in the distribution of TSAP-positive strains of S. aureus. Overall, 39 (14%) were TSAP positive by both methods. The earliest positive strain was an isolate submitted in 1957. TSAP-positive strains were most prevalent in the group of isolates submitted in 1976 for which 29% reacted, but the percent positive subsequently declined for isolates submitted in later years. TSAP production was more frequent among strains of phage types 29, 29/52, and 52 than among other strains. The use of IEF to identify TSAP detected false-positive proteins. Seven strains were positive by IEF and negative by solid-phase radioimmunoassay, whereas only one was positive by solid-phase radioimmunoassay and negative by IEF.