Mutans streptococci (ms) and lactobacilli levels were determined by conventional and commercial dip-slide methods in three groups of young subjects, aged 5-6 years (93 subjects), 12-13 years (78 subjects) and 18-20 years (81 subjects). Using the same paraffin-stimulated saliva samples, ms and lactobacilli were estimated by conventional viable counts on modified mitis-salivarius agar (MSB) and Rogosa agar plates, and by inoculation of Dentocult SM and Dentocult LB dip-slides (Orion Diagnostica, Finland). The salivary ms and lactobacilli counts obtained from conventional agar plates were significantly correlated (P < 0.0001) with the dip-slide estimates of these organisms (Kendal Tau = 0.56, 0.71 respectively). Subjects in Group 2 showed the highest proportion (77 per cent) of individuals with salivary ms levels above 2.5 x 10(5) cfu/ml saliva; 99 per cent of that group had detectable levels of lactobacilli. Significantly different median salivary ms and lactobacilli levels were demonstrated between all groups except for lactobacilli levels between Groups 2 and 3. These dip-slide tests provided suitable and simple methods for screening salivary lactobacilli and ms levels which may have a useful role in the assessment of caries risk.