Six Arena sterilis L. introductions were crossed in a diallel to study groat protein level and to estimate heterosis and types of genetic effects for percent protein and protein yield. Parents, one set of Fl's, and two adapted commercial check cultivars were grown for three seasons (1969‐1971) along with reciprocal Fl's in 1970 and with F2's in 1970 and 1971. The A. sterilis parents averaged 25.6% groat protein and the two check cultivars, 17.9% groat protein. The adapted check cultivars produced twice as much seed yield, which resulted in a higher yield of protein. Percent groat protein in the F1 and F2 was similar to the midparent values. Heterosis for protein yield averaged 10.7% in the F1 but was much reduced in the F2 generation. Reciprocal F1 hybrids did not differ for percent groat protein or protein yield. General combining ability predominated for all characters. Partial dominance occurred for percent groat protein in this group of genotypes. Epistasis and environmental factors were important for protein yield. The relationship between protein and protein yield was generally not significant, but tended to be negative.