The control of flowering time is one of the most important properties governing geographic distribution of crop plants.  Previous studies have shown that a series of genes known as the e-gene series is responsible for control of the flowering process in soybean.  A greater understanding and ability to manipulate this gene series may have major economic benefits.  Among the E genes, the E1 gene has been found to have the greatest impact on soybean phenology.  The time from vegetative development to flowering can be broken down into four phases: a photoperiod-insensitive pre-inductive phase, a photoperiod-sensitive inductive phase, a photoperiod-sensitive floral development phase and a photoperiod-insensitive floral development phase. The goal of this study is to investigate the role of the E1 gene in how soybean transitions from vegetative to reproductive development.    Two near isogenic lines (NIL) that differ for the allele at the E1 locus were grown in a reciprocal transfer experiment under short (12 h) and long day (20 h) conditions.  The plants were observed throughout early development to determine the difference between dominant and recessive E1 alleles in terms of the four phases leading to flowering and the differential response to photoperiod.  Under the short day treatment both NIL behaved similarly. The pre-inductive phase is identical for the two NIL and under both photoperiods.  Under the long day treatment, both photoperiod-sensitive floral induction and development phases appear to be delayed by the presence of the dominant E1 allele.