In normal growth conditions, total protein percent (salt soluble plus hordein fractions) in the endosperm at maturity in barley cultivar Hordeum vulgare L. cv 'Ruth' was about 14%, whereas in an accession of wild barley, Hordeum spontaneum Koch line 297, it was about 28%. Spike culture experiments were conducted to ascertain whether there were basic differences between the two genotypes under conditions of widely different nitrogen supply. Spikes of each genotype were grown from 8 to 25 days after flowering in in vitro culture in a growth medium containing 0 to 4 grams per liter nitrogen supplied as NH4NO3. Spikes were pulse-labeled at intervals from 12 to 24 days after flowering with 3.7 megabecquerel of [3H]leucine to determine relative rates of synthesis of hordein-1 and hordein-2 polypeptides. At low nitrogen levels 'Ruth' had a lower protein content than 297, but at increasing nitrogen levels its protein content increased rapidly and reached a maximum (35%) higher than 297 (30%). The relative contribution of the hordein fraction to total protein increased mainly with time, and hordein-1 to total hordein increased mainly with nitrogen level, in both genotypes. There appeared to be no fundamental limitations in the capacity of 'Ruth' to accumulate protein; 297 appears to have a greater basal level of nitrogen availability under normal conditions.