||Old World bluestem (OWB; Bothriocloa spp,)are popular in the southern Great Plains but little is known about the relationships between forage characteristics and animal productivity. The influence of differences in herbage mass and sward height of OWE on rate of gain during the summer grazing season was examined during 2 years at El Reno, Okla, Soils were fine, silty Pachic Haplustolls of the Dale series. Swards of caucasian [B, caucasica (Trin,) C, E, Hubb,] and ’Plains’ [B, ischaemum var ischaemum (L,) Keng,] OWE were maintained at different levels of forage mass (low, medium, and high) by continuous variable stocking and were grazed from mid- May to late September by steers with an initial weight of about 225 kg, Weight gains were depressed in late August, but in 1985 gains recovered due to late season rains. Season-long gains averaged 0.61 kg day(-1) in 1984 and 0.69 kg day(-1) in 1985, Daily gains of steers increased linearly with increased herbage mass (P < 0.05), but slopes were different due to a year X species interaction. Daily gains peaked at a herbage height of 41 cm in 1984, but increased linearly throughout the range of the data (75 cm) in 1985, Individual animal gains decreased linearly with increasing stocking rate such that maximum gain per hectare was achieved at about 5 animals ha(-1) (standard 500 kg), The data suggest that maintaining higher herbage mass and height of OWE forage improves animal performance and support the practice of intensive early grazing and removing cattle by late July when rate of gain declines.