Cultivar emergence base (CEB) temperatures were calculated for the tomato (Lycopersicon esculentum Mill.) cvs. G-18824 and H2134 and their hybrid progenies. Each population required a mean accumulation of 160 daily heat units above their CEB. The early emerging parent had a low CEB of 42.6°F, the late emerging parent had a high CEB of 46.1°F, and their progenies were intermediate. The CEB of each cultivar and progeny was the same at different temperatures. Inheritance was found to be quantitative and an estimated 24 gene pairs differentiated the parents for CEB. There was strong evidence for additive gene action. Dominance and epastasis were not ruled out. Broad sense and narrow sense heritability estimates were 25-40% and 25% respectively. The same gene system appears to control emergence at both low and high temperatures. Selection for emergence at low temperature could be achieved at high temperatures on the basis of CEB.