The effect of selection for high seed protein content on plant development in soybeans (Glycine max (L.) Merr.) was investigated by comparing the lengths of growth stages of four selected populations with those of a nonselected control. Each population, grown at two locations in one season, was a composite of four crosses between G. max and its putative wild ancestor, Glycine soja Sieb. and Zucc. The growth stages were planting to emergence, emergence to flowering and flowering to maturity. The length of each growth stage was measured in soybean development units (SDU) and in days. On average, populations selected for protein alone required more SDUs from planting to emergence and from emergence to flowering and fewer SDUs from flowering to maturity than did the control. The mean temperature in the stage from flowering to maturity was negatively correlated with protein content in all populations. The correlations ranged from −0.22* to −0.34**.