Streptococcus godonii gave rise t o &haemolytic variants (Bhp+ for beta--haemolysin production) at frequencies of 104-10-3 on agar medium containing washed horse erythrocytes. Bhp+ variants reverted t o the wild-type ahaemolytic phenotype (Bhp-) at the same frequencies. There was a significant probability ( 2 01) that phase variation in Bhp and phase variation in the previously described Spp (sucrose promoted phenotype) would occur concomitantly, but there was no correlation between these phenotypes. There was evidence also of independent phase variation in adhesion to saliva-coated hydroxyapatite (Asp for adhesion t o salivary pellicles), in lactose-sensitive coaggregation (CIS for goaggregation, lactose-sensitive) and in the concentrations of particular cell surface antigens (Cap for gel1 antigen profile) in strains that had undergone phase changes in Spp and/or Bhp. Phase variation in all these phenotypes were transitions between high and low levels of activity and each appeared t o occur as an independent event. Significant associations (P c< 00001 by contingency table analysis) between particular phenotypes such as Bhp and Asp and between Asp, CIS and Cap phenotypes, however, were apparent. The results suggest that S. gordonii cells become predisposed t o phase variation and that the resulting independent phenotypic changes may give rise t o phenotypically diverse streptococcal populations able t o accommodate rapid and transient environmental changes in the mouth.

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