- Tall fescue often results in poor liveweight gains. This may be accounted for by variations in perloline content, nitrogen content, or digestibility of the plant. Two groups of tall fescue plants were examined for each of these traits. These groups consisted of (a) fifteen single-crosses of a six parent diallel and (b) seven cultivars of tall fescue. The diallel cross was planted at Corvallis, Oregon and Columbia, Missouri. Plots were harvested and sampled on April 8 and September 22, 1975 at Corvallis; Oregon and on October 16, 1975 at Columbia, Missouri. The two cuttings at Corvallis, Oregon and the fall cuttings at Corvallis and Columbia were analyzed as multiple environments. The cultivars were planted at Corvallis, Oregon and harvested April 10, July 11, and September 22, 1975. All samples were analyzed for perloline and nitrogen content. Samples from the fall harvests at Corvallis, Oregon and Columbia, Missouri were analyzed for in vitro digestibility. There were significant differences among crosses for perloline content. Significant general and specific combining ability was found for perloline content. Broad-sense heritabilities (H[subscript B. S.] = .21-.94) tended to be larger than narrow-sense heritabilities (H[subscript N.S.] = .15-.53). There appeared to be a high degree of dominance for low perloline. Significant differences existed among the cultivars for perloline content. Dates of harvest were a significant source of variation for perloline content, with perloline increasing steadily over the season. Significant genotype x environment interactions were found, suggesting that lines should be tested over locations and years. It should be possible to select for low perloline lines with a program of recurrent selection using a high perloline tester. Significant differences were found among crosses for nitrogen content. General combining ability was significant in all cases. Narrow-sense heritabilities (H[subscript N.S.] = .50-.72) were almost as large as the broad-sense heritabilities (H[subscript B. S.]= .55-.89), suggesting primarily additive gene action for nitrogen content. No differences were found among the cultivars for nitrogen content, but cuttings were a significant source of variation. Differences among cuttings as well as the cutting x cultivar interaction appeared to be due to soil fertility levels and disease. Selection for nitrogen content should be possible with recurrent selection. Lines should be tested over environments. There were differences in in vitro digestibility among crosses for the September harvest at Corvallis, Oregon, but not for the October harvest at Columbia, Missouri. General combining ability was a significant source of variation. The broad-sense heritability (H[subscript B. S.] = .74) was high. The narrowsense heritability (H[subscript N.S.] = .18) was very low, however, indicating that in vitro digestibility was controlled primarily by nonadditive gene action. Digestibilities were significantly higher at Corvallis, Oregon than at Columbia, Missouri. No genotype x environment interaction was found. Selection for high in vitro digestibility should be possible with a program of recurrent selection for specific combining ability.