An indirect fluorescent antibody technique was developed to identify Campylobacter spp in lesions of swine proliferative enteritis (SPE). Rabbit antisera to C hyointestinalis and C sputorum subsp mucosalis were produced. Bacterial smears stained by fluorescent antibody test with homologous antisera differentiated C hyointestinalis from subsp mucosalis. Ileal frozen sections from 29 pigs with histologic lesions of SPE had specific fluorescent staining of C hyointestinalis in all 29 and subsp mucosalis in 24. Bacterial structures of C hyointestinalis were seen in large numbers and were broadly distributed in intestinal luminal exudate, mucosal necrotic tissues, surface epithelium, lamina propria, and proliferative cryptal epithelium. Numerous C hyointestinalis organisms were always present in the apical cytoplasm of proliferative cryptal epithelium. Fluorescent subsp mucosalis bacteria were seen less frequently and were distributed focally in the mucosa. Numerous subsp mucosalis organisms were more common in cellular debris and in necrotic tissues of surface mucosa, and less common in the epithelial cells of proliferative crypts. Ileal sections from 13 pigs without SPE had no fluorescent staining of C hyointestinalis and subsp mucosalis.