Japanese brome (Bromus japonicus Thunb.), an introduced annual grass, is now common in some northern mixed-prairie communities. This species has the potential to alter both the seasonality of standing crop and forage quality. We sought to gain a greater understanding of Japanese brome seed germination by subjecting seed to a series of 55 constant or alternating temperature regimes following 3 to 9 months of dry laboratory storage. Cold and moderate temperature regimes provided optimum germination conditions (defined as not lower than the maximum observed minus one-half its confidence interval at the 0.05 level of probability). Extremely cold or warm temperatures suppressed germination. Germination of afterripened seed over a wide range of temperature combinations, many of which occur during fall in the Northern Great Plains, should enhance establishment and perpetuation of Japanese brome on rangelands.