Studies of the amount of outcrossing in alfalfa seed fields, as affected by flowering alfalfa, distance, and size of plots, at Davis in 1965 and 1966, indicated that field size probably contributed more toward minimizing contamination than the other factors. However, some evidence indicated that flowering alfalfa, and distance, also reduced the amount of outcrossing. These studies were made in Ranger alfalfa and a white-flowered type.