In field experiments with young spaced plants of 48 soybean (Glycine max (L.) Merr.) cultivars, derived lines tended to have higher rates of apparent photosynthesis (PA) than their parent lines over 3 yr of tests using the 14CO2 method. For 2 yr in which chlorophyll and specific leaf weight (SLW) were also measured, a significant number of derived lines had higher PA, chlorophyll and SLW than their parent lines. With 12 cultivars of similar maturity, grown as row-crop tests for 4 yr, PA and leaf percent N were correlated with each other during August (pod-filling period) but not during July (flowering period). August PA and leaf percent N were correlated with bean yield, but July values were not. Chlorophyll and SLW were correlated with each other in July and in August; each was correlated with PA in July but not in August. Although July measurements of leaf characters were not correlated with bean yield, July and August values were correlated for PA and for chlorophyll. The correlations observed among the characters in different sampling periods are discussed in relation to possibilities for selection.