The relationship between level of night temperature and cessation of growth and the effect of cumulative cold nights on the continuation of growth in Cenchrus ciliaris, Chloris gayana, Panicum maximum var. trichoglume, P. coloratum var. makarikariense and Pennisetum clandestinum was examined in two experiments. Estimated critical mean daily temperatures causing cessation of growth of buffel, green panic and Makarikari grasses were about 12°C and for Rhodes and Kikuyu were about 8°C. However, with a day temperature of 20°C, 'critical' night temperatures of all species were below 4°C. Where the night temperature was decreased from 14 to 4°C, significant decreases in net assimilation rate (EA), but not leaf area ratio (FA), occurred after 5 days in C. ciliaris and P. maximum. Over a period of 10 consecutive exposures to a night temperature of 4°C there was a significant decrease in relative growth rate (Rw) but no apparent adaptive change in either Rw or EA. Leaf stomatal resistance (rs) in these same species, however, was decreased in successive photoperiods (at 23°C) following continued exposure to 4°C at night. After 10 days, the mean rs values were significantly higher following 4°C than 14°C nights in C. ciliaris, P. maximum, C. gayana and P. coloratum, but not in P. clandestinum.