Peptic-tryptic-Cotazym (PTC) digests were obtained, simulating in vivo protein digestion, from rice, maize, rye, oats, barley, and sorghum prolamines and tested on small intestine cultures from rat fetus. The PTC digests of the prolamine fractions from rice and maize, even when tested at a concentration as high as 0.5 mg/ml, did not affect in vitro differentiation and maturation of fetal rat jejunum that took place in vitro in a way comparable to what happens in vivo. On the contrary, the PTC digests of prolamines from rye, oats, barley, and sorghum were very active in slowing down in vitro development of fetal rat intestine. These results further strengthen earlier findings and all together show that there is a strong correlation between toxicity results of cereal and/or cereal components assessed with clinical trials or in vitro systems based on bioptic specimens of intestinal mucosa from celiac patients and with the culture of rat fetal intestine. Therefore, the rat fetal intestine culture is considered to be an adequate model for screening and investigating cereal peptides which are toxic for the celiac small intestinal mucosa.