A radioimmunoassay for the detection of serum swine pepsinogens is described. The sensitivity and reproducibility of the assay were satisfactory for its clinical use. In normal pigs, the serum pepsinogen level was 1.51 +/- 0.56 ng/mL. Cases with parakeratosis, erosions and ulcerations of the pars oesophagea had elevated pepsinogen levels (5.15 +/- 1.98 ng/mL).