A 4-year longitudinal study of the oral prevalence of enteric gram-negative rods and yeasts in 116 Chinese primary school children in Hong Kong was conducted. The oral prevalence of enteric gram-negative rods for each consecutive year was 25.3%, 37.0%, 24.0% and 25.8% respectively, with a weighted mean of 27.9%. Enterobacteriaceae, which comprised 57% of all enteric gram-negative rods, were more common in children with no caries experience. The oral prevalence of yeasts for each consecutive year was 7.7%, 12.0%, 14.4% and 15.5% respectively, with a weighted mean of 12.5%. Candida albicans comprised 84% of all yeasts isolated. Oral yeast carriage was significantly associated with caries prevalence. While the oral prevalence of enteric gram-negative rods in primary school children in Hong Kong may be higher than in other parts of the world, repeated isolation of either enteric gramnegative rods or Candida spp. from individual children over the 4-year study period was rare, suggesting that carriage of these organisms is transient.