Comparisons were made of the accumulation of dry matter in the various plant components of a determinate (D66‐5566) strain had an indetermate (‘Kent’) soybean [Glycine max (L.) Merrill] cultivar using field‐grown plants for 2 years at Lexington, Ky. Kent and D66‐5566 are of similar maturity and yielding ability.At initial flowering D66‐5566 had reached 84% of its maximum height, compared with 64% for Kent. At this point the stem dry weight of D66‐5566 was 67% of the maximum compared with 30% for Kent. Although stem elongation of the determinate type was nearly complete when flowering began, it continued to increase in dry weight.At initial flowering Kent had produced 58% of its total vegetative material, compared to 78% for D66‐5566. Both types produced very little vegetative growth after a measurable amount of dry weight had accumulated in the pods and seeds. Kent produced more vegetative material during flowering and pod set, and the potential for competition for photosynthate between reproductive and vegetative growth was greater.The rate of accumulation of dry matter in the pods and seeds was greater for D66‐5566 than Kent in 1970, but there was no significant difference in 1971. The rates of both types were greater in 1970 than 1971, although grain yields were greater in 1971 than 1970. The length of the effective filling period, i.e., the grain yield divided by the rate of grain filling, was longer for both types in 1971 than 1970, and was thus positively associated with grain yields.