Antibiotic usage and improved living conditions may have contributed to a dilution of "rheumatogenic" strains of group A streptococci and to their replacement by attenuated streptococci with less rheumatogenic potential. Whether this is due to decreased virulence or to loss of specific bacterial antigens or toxins in prevalent strains is not yet known. The pneumococcus, which has been moderately resistant to antibiotics only in isolated cases, has appeared in South Africa in strains that are highly resistant to at least five major antibiotics; plasmid transmission of resistance is suspected. The newly available pneumococcal vaccine may become very important if such strains spread. Gonococci isolated from urogenital lesions have developed only moderate drug resistance. Gonococci causing disseminated infection have retained their exquisite sensitivity to penicillin; the most virulent strains are associated with greatest sensitivity. However, the newly discovered penicillinase-plasmid in gonococci is transferable to these virulent strains as readily as to others.