Three near‐isogenic lines (isolines) of ‘Clark’ soybeans [Glycine max (L.) Merrill] differing greatly in pubescence characteristics (dense pubescent, normal, and glabrous) were subjected to water stress during flowering or podfilling stage under field conditions. During these developmental stages, apparent photosynthesis (AP) rates of fully expanded top leaves were measured using a single leaf chamber, and water potential was determined on the same leaves using the pressure chamber technique. AP rates decreased linearly as leaf water potential decreased. The decrease was less during the flowering stage than during pod‐filling stage for all three isolines. Under nonstressed conditions (—1 bar soil water potential), AP rates for normal, dense pubescent, and glabrous were 119.8, 73.4, and 76.0% higher during pod‐filling stage than during following