Enzyme-linked immunosorbent assay examination of sera from pigs vaccinated with T. spiralis nativa infective larvae and/or challenged with T. spiralis spiralis larvae using a T. spiralis spiralis excretory-secretory antigen showed a significant cross-reaction between the two species of Trichinella. Eight of 12 pigs vaccinated with a high dose of T. spiralis nativa reacted positively 28 days postvaccination while the remaining four pigs had high but negative ELISA optical density readings. Five of six pigs challenged with the homologous species reacted positively 28 days postchallenge but the sixth pig remained negative despite having a muscle infection of 5.6 larvae/g of musculature.