Relationships between groat-protein percentage (PP), grain yield (GYD), and protein yield (PYD) of oats were studied using F(,2)-derived lines in the F(,3) and F(,4) populations from 27 matings between high-protein and high-yield lines. The high-protein parents included (a) selections from an Avena sativa bulk, (b) selections from three-way matings in which an initial parent was A. sterilis, and (c) commercial cultivars. The high-yield parents were derived from backcross populations involving A. sterilis donor parents;Significant genetic variability existed among F(,2)-derived lines for PP, GYD and PYD in all matings except one for PP. Progeny means and midparent values for PP, GYD, and PYD in 5, 12, and 16 matings, respectively suggested additive gene action was operating for these traits. Design II analyses of 23 matings indicated the importance of additive effects for GYD genes and additive and nonadditive effects for PP and PYD genes. Mean heritabilities on a plot basis for the matings ranged from 0.11-0.63 for PP, 0.11-0.43 for GYD, and 0.10-0.44 for PYD;PP had a highly significant negative correlation with GYD (-0.33**) overall, but in five matings, these traits were not significantly correlated. Overall, PP had a small significant negative correlation with PYD (-0.09**) and PYD and GYD had a high positive association (0.98**). F(,2)-derived lines with both high PP and high GYD were obtained;High transgressive segregates occurred in two matings for PP, in nine for GYD, and in 14 for PYD. These high transgressive segregates in many cases were probably due to epistatic interactions;Comparisons of high transgressive segregates for PYD with their mating midparent values showed that increases in PYD were due to either increases in GYD only or concurrent increases in PP and GYD. In four matings, high transgressive segregates for PYD were due to increases in both PP and GYD, with up to 57% of the increase due to PP. In 12 matings, high transgressive segregates for PYD were due to increases in GYD alone;Specific genetic combinations of high-protein and high-yield parents were important in determining which matings produced the highest PPs, GYDs, and PYDs. These traits are moderately heritable, so genetic variability for both PP and GYD should be exploited in selecting for high PYD.