Six variables which are capable of measurement at the chairside were assessed for their ability to identify children who would experience high caries increments during the subsequent 2 or 3-year period. The predictor variables measured in 84 urban schoolchildren, aged 11-12 years at baseline, were: baseline caries experience, salivary buffering power, counts of salivary Streptococcus mutans and lactobacilli, and two estimates of between-meal sugar intake. All the predictor variables showed statistically significant correlations with either 2-year or 3-year caries increment. Approximately 25% of subjects were identified as high risk individuals on the basis of a 2-year DFS increment of 5 and above, or a 3-year increment of 8 and above. None of the predictor variables achieved the target predictive value of 80%, either individually or in combination. The combination of Streptococcus mutans counts and buffering capacity measurements at baseline correctly identified low risk during the 3-year period in 78% of individuals (specificity), but only identified 12 out of 19 individuals (63%) at high risk (sensitivity), giving a predictive value of 75%. The predictive value for baseline caries experience was 66%. The results of the present study indicate that the salivary diagnostic tests have potential, but need further development before they can be used with confidence in clinical practice.