Concentrations of IgA, IgG, IgM, and IgA subclasses were measured in 138 pairs of parotid gland saliva (PS) and labial gland saliva (LS), using an enzyme-linked immunosorbent assay (ELISA) technique in which levels of Ig were quantitated using affinity-purified anti-heavy chain reagents for capture and development. Both PS and LS were collected simultaneously during sour lemon drop stimulation. As previously observed, IgA was the dominant immunoglobulin in both salivary fluids, the concentrations of which were highly correlated within the subjects studied. The mean proportion of IgA1 to total IgA was slightly higher in LS (0.66), compared with PS (0.60). Little IgM was usually detected in either secretion. In contrast, LS had IgG concentrations (mean, 8.1 micrograms/ml) which were significantly higher (P less than 0.001) than those found in parotid saliva (mean, 0.3 micrograms/ml). Over 30% of the subjects had mean LS IgG levels above 10 micrograms/ml. The mean percentage of LS IgG to IgA was 20% in the 138 samples tested. Gel filtration of pairs of PS and LS from four individuals revealed IgM, IgA, and IgG to elute in positions commensurate with pentameric IgM, secretory IgA, and monomeric IgG. Little or no monomeric IgA could be detected. These results suggest that, in addition to IgA, the IgG isotype may also be important in antibody-mediated phenomena which occur in oral microenvironments bathed by minor salivary gland secretions.