A group of glycoproteins, which strongly bind peanut agglutinin (PNA) was found in Eimeria tenella. Two major antigenic glycoproteins, Et110gp and Et35gp, were identified in sporulated oocysts and sporozoites. Molecular characterisation of carbohydrate moieties (lectin binding, enzymic hydrolysis and monosaccharide composition) revealed that both glycoproteins are rich in galactose and N-acetylgalactosamine, and appear to be sialylated. Both glycoproteins were susceptible to treatment with neuraminidase followed by O-glycosidase, suggesting that the oligosaccharide chains are attached to the protein by an O-glycosidic linkage to serine and/or threonine. Purified Et35gp contained a large number of serine (14) and threonine (33) residues, and was rich in glycine. This protein aggregated after repetitive lyophilisation and migrated on SDS-PAGE gels as an 85,000 protein. Sera against purified Et35gp raised in chickens and rabbits, and anti-E. tenella immune chicken serum recognised both antigens on blots and on the surface of sporozoites. Chickens immunised with purified Et35gp were not protected against coccidial infection.