The coeliac active peptide B 3142, which has been isolated from a peptic-tryptic digest of gliadin and which consists of 53 amino-acid sequences, was partially hydrolyzed with alpha-chymotrypsin. The two fragment peptides CT-1 (positions 1-22 of B 3142) and CT-2 (positions 23-53) were separated by high-performance liquid chromatography on octadecyl silica gel and purified by gel filtration on Biogel P2. The examination in the organ-culture test including 18 coeliac patients on normal diet and 7 control persons have shown that the toxicity is preserved after the chymotryptic treatment and that the peptides B 3142, CT-1 and CT-2 do not significantly differ from one another according to their coeliac-specific effect.