Amino acid composition of Hiproly barley suggested greater nutritional value of the protein for animals as compared with a sister line isogene and naked Compana barley. In two growth trials, female weanling rats fed Hiproly barley gained faster, more efficiently and had higher protein efficiency ratio values than equivalent animals fed the other two barleys. Rats fed a cornstarch-casein control diet were superior in performance to all barleys in one trial but were equaled by rats fed Hiproly barley in the second trial. Nitrogen balance studies with young and mature female rats validated the superior protein quality of casein as compared to barley protein. Hiproly barley had less digestible nitrogen than Compana barley for young and mature rats and less than Hiproly Normal barley for immature rats. Compana barley was found to have a higher apparent biological value than Hiproly barley, although rat growth performance indicated otherwise.