624 Staphylococcus aureus strains from our clinical laboratory were screened for toxic shock syndrome toxin 1 (= TSST-1) production and 16.7% of the strains were found to be positive. TSST-1-positive strains were isolated from material which originated from males and females with the same frequency. The strains were found in swabs from the respiratory tract, the conjunctiva, in sputum and wounds. TSST-1-positive strains were more resistant to arsenate and cadmium ions than non-producers; their sensitivity to the antibiotics (when tested), was no different. The toxin-producing strains were lysed above all by the bacteriophages 29, 52, 80, 55, 75 and 83A. We isolated 19 S. aureus strains from 321 vaginal swabs: one of these strains was TSST-1-positive. Most of the strains were found in swabs from women using tampons. It has been concluded that the infection with TSST-1 positive S. aureus is either of subclinical course or that in most of the cases, the syndrome is of a less dramatic course than usually described. Quite certainly the syndrome is underdiagnosed in Germany.