Soybean cultivars representing each of the 10 U.S. Maturity Groups (MGS) (00 to VIII) were screened for the photoperiodic response to flowering from March, 1974 to June, 1974; another set was screened from October, 1974 to January, 1975 using natural daylength in the field as the short-day treatment. In another distant field artificial light was used to extend the natural daylength to 16 hr which represented the long-day treatment. In the March screening, l,898 cultivars were screened while in October, 1,547 cultivars were screened.