Double antibody sandwich enzyme-linked immunosorbent assays (DAS-ELISA) have been developed for the assessment of IgM, IgG and IgA concentrations in porcine serum. Isotype-specific monoclonal antibodies (mAb) were used for coating and detection. The DAS-ELISAs were examined for their ability to detect each isotype and for the assay variations. A computer programme was used to verify the parallelism of the slope of each serum sample with the slope of standard/reference serum, a prerequisite for reliable estimation of Ig concentrations. The DAS-ELISAs are easy to perform and highly specific, have adequate detection levels (ranging from 7 to 50 ng ml-1) and are very reproducible, as illustrated by the inter- and intra-assay variation coefficients (ranging between 4.9 and 7%). To illustrate the applicability of the ELISAs we assessed Ig concentrations in pig sera sampled from birth to young adulthood.