The potential release of transgenic wheat (Triticum aestivum L) cultivars is raising concerns over the possibility of in-field contamination by outcrossing (OC), via pollen mediated gene flow (PMGF) between transgenic and conventional wheats. A two years study was conducted with the objective to examine the effects of varying spatial isolation distances on OC of four hard red spring wheat cultivars. ‘Purendo-38' wheat, which is dominant for blue aleurone (BA) seed, was used as the pollen source and phenotypic marker to record successful OC events. The study was conducted at Prosper, ND in 2003 and 2004; and at Carrington, ND in 2004. In 2003, no OC could be detected. We believe that this could be the results of many factors acting alone or in combinations. The unfavorable weather conditions for OC during flowering stage and shortage of BA pollen due to the small amount of BA seed planted might be the two major reasons. In 2004, however, OC occurred at both locations. At Prosper, OC was observed in all four cultivars and all directions from the BA. Up to 7.8% OC was observed at 0.3 m distance from the BA pollen source. Cultivars varied significantly for observed OC levels, with Granite exhibiting the highest OC, followed by Alsen, Explorer, and Oslo, respectively. At, Carrington, OC observed was less than at Prosper. Only one OC event could be detected at a distance of 1.5 m from the BA pollen source. Spatial isolation distance and wind direction affected long-distance gene flow at both locations. Results from this study indicate that pollen synchronization and environmental conditions during the period of flowering were the most critical components affecting OC.