Two recently developed enzyme immunosorbent assays (EIA) for the detection of significant titre increases in enteroviral IgG-antibodies were evaluated as diagnostic tools in 127 etiologically well-characterized patients with aseptic meningitis. One assay was based on heat-treated virions (H-EIA) and one on synthetic peptides (P-EIA) as antigens. The sensitivities, with virus isolation as reference method, were 0.67 by H-EIA and 0.62 by P-EIA, which were higher than by a routinely used complement fixation test (CFT, 0.51) but somewhat lower than the sensitivities found by two previously presented IgM-assays, mu-capture EIA, and solid-phase reverse immunosorbent test (SPRIST). The specificities of the two IgG-EIA techniques and CFT were apparently high, whereas the two IgM-assays showed positive reactions in some non-enteroviral cases. A relatively rapid increase in enteroviral IgG-antibodies was apparent using H-EIA and P-EIA. The two IgG-EIA tests contributed with considerable additional etiological information since significant IgG-rises were obtained in 13 patients by H-EIA and in 19 by P-EIA, respectively, out of the 56 individuals in whom enterovirus isolation was negative and a non-enteroviral diagnosis was not found. Thus, detection of enteroviral IgG-antibodies by H-EIA and P-EIA seems to be a valuable alternative to CFT for the routine diagnosis of enteroviral meningitis. The IgM-assays, mu-capture EIA, and SPRIST, may allow a relatively rapid report of an enteroviral infection. However, since both the IgM-tests are hampered by incomplete specificities, a confirmation of positive results by an IgG-assay should be carried out.