A follow up study was carried out to determine the kinetics of appearance of surface/stichosomal (S/S) components, recently included in the TSL-1 group of Trichinella spiralis muscle larva (ML), in serum samples from 13 experimentally infected pigs. Detection of circulating antigens in these animals was done by a sandwich enzyme-linked immunosorbent assay (ELISA) using T. spiralis specific rabbit polyclonal immunoglobulins to capture free antigens and monoclonal antibody NIM-M1 to recognize S/S antigens. The assay developed was able to detect as little as 35 ng ml-1 of S/S components added to normal pig serum. Antigenemia was observed in 54% of the experimentally infected swine with two peaks of appearance, one early at 1-4 weeks post-infection (pi) and one late at 10-14 weeks pi. Specific antibodies against S/S components were demonstrated in serum samples from all experimentally infected pigs starting at 3-4 weeks pi. Free antigen was also detected in serum samples from naturally infected backyard pigs with a sensitivity of 56% compared with 94% when antibody production was determined using purified S/S components in an ELISA.