Previously, we showed that human submandibular-sublingual (SMSL) salivas contain one or more proteins, Mr circa 300,000 daltons, which specifically promote adhesion of Streptococcus mutans serotype-c strains to hydroxyapatite. Also, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that the adhesion-promoting proteins (APPs) exhibit heterogeneity. The aims of the present study were to determine whether APPs are generally present in human SMSL salivary secretions and to characterize the noted heterogeneity. Acid-stimulated SMSL saliva samples were obtained from 54 Japanese subjects, and Mr values were obtained by SDS-PAGE. APPs were present in all saliva samples examined, though at significantly different concentrations. The APPs occurred as either single (20 subjects) or double bands (34 subjects), with a mean Mr (88 bands) of 297 kD and a range of 248-338 kD. A plot of the frequency distribution of the APPs according to Mr showed a trimodal distribution, with mean Mr values, standard deviations, and ranges for the three groups being 265 (S.D., 6.9; range, 248-278), 293 (S.D., 6.7; range, 280-305), and 320 (S.D., 7.0; range, 310-338) kD. Variations of Mr within groups may be attributed to experimental variation, although microheterogeneity cannot be excluded. Differences between groups can best be explained in terms of three polymorphic proteins, with low (L), intermediate (I), and high (H) Mr values. Six phenotypes were detected with L, I, H, LI, LH, and IH Mr bands. A Hardy-Weinberg analysis showed that the phenotype data fit a single-gene, three-alleles model.(ABSTRACT TRUNCATED AT 250 WORDS)