The amount and speed of water absorbed in natto soybean [Glycine max (L.) Merr.] soaking is important for the quality of the finished product.  This study was conducted to examine the extent of genotype, environment and genotype x environment interaction effects on water uptake parameters.  A recombinant inbred population was generated from a cross between OT91-3 (slow soaking) and AC Colibri (rapid soaking).  The parents, two natto checks and 54 RIL lines were grown at Ottawa from 2003 to 2005.  Water uptake observations were taken at 0, 2, 4, 6, and 24.5 h using seed from individual plots.  The exponential rise to a maximum equation, Y = a(1-exp(-bX)), was fitted for each plot, and the parameters a at 16 h (a16) and b, as well as seed composition and agronomic traits were subjected to an analysis of variance.  Genotype, genotype x year and genotype-within-year effects were significant for these parameters.  Heritability estimates for water uptake parameters were low to moderate on a plot basis.  Work is ongoing to identify quantitative trait loci associated with these parameters.