Early gnotobiotic caries experiments have been done in mono-association, although natural caries is always the result of bacterial interactions. In 2 experiments, 4 groups of 8 weanling germ-free O–M rats were mono-associated with Strep, mutans GS5 or Strep, sanguis 34, or one of these streptococcal strains was inoculated in di-association with V. alcalescens OMZ 193. Two y-irradiated powdered semi-synthetic diets with 16 or 40% sucrose were given for 30 days. Di-association of the streptococcal strains with V. alcalescens resulted in caries activities on the 16-percent sucrose diet significantly lower (pf alcalescens between masses of streptococci, deep in fissures and smooth surface plaque.