Nine Hordeum spontaneum lines of Middle Eastern origin were mated in an incomplete factorial with three elite N. American lines of H. vulgare and the F(,1)s were then recurrently backcrossed to their H. vulgare parents for up to four backcross generations. In each generation, approximately thirty F(,2)-derived lines from each mating were evaluated at three locations in Iowa during 1981;Gene action, on a generation mean basis, was almost completely additive for grain yield, biomass, straw yield, harvest index, and growth rate index, whereas both additive and epistatic types of gene action were important for height and heading date. The decrease in genetic variance over backcross generations for all traits but grain yield was consistent with simple gene action models having predominantly coupling linkage. For grain yield, however, genetic variance increased in the first two backcross generations, indicating either a strong positive relationship between genetic variances and means and/or the disruption of a few repulsion phase linkages involving alleles with major effects;Transgressive segregates for grain yield increased with each backcross generation, ranging from 0.0% in the BC(,0) to 9.1% in the BC(,4). By comparison populations of about thirty lines of each recurrent parent had a mean of 3.5% transgressive segregates. The nine H. spontaneum parents differed substantially in percentage of transgressive progeny, with a range of 1.7 to 9.6% in the BC(,2) through BC(,4); however, all nine parents were represented in the parentage of the top fifteen segregates in the study;Performances of the H. spontaneum lines, per se, were generally good predictors of progeny performance. Mean grain yields of the lines, per se, had a correlation of 0.7 with their means inter se, and a correlation of 0.5 with the mean percentage of their progeny in the BC(,2) through BC(,4) that yielded above the recurrent parent mean (ARP). However, predictive criteria based on performance, inter se, usually gave higher precision; the correlation between general combining ability estimates for grain yield in the BC(,0) with ARP was 0.7. The increases in grain yield were obtained at no apparent cost in agronomic type. Compared with their H. vulgare parents, the superior segregates were clearly more vigorous, having higher grain and straw yields; however, they had similar values for height, heading date, and harvest index, and essentially the same seed characteristics.