Preliminary studies with controlled pollinations have shown that pistillate flower abscission (PFA) in walnut (Juglands spp.) is associated with heavy pollen loads on the flowers. This study measured percent pistillate flower abscission (PFA), pollen grains per flower, yield and yield efficiency on Serr walnut from trees adjoining pollinizing cvs and at sequential intervals up to 197m away in twelve orchard locations. A highly significant, negative correlation in PFA existed as distance from the foreign pollen source increased. Pollen grains per flower were highly correlated with percentage PFA. Yield and yield efficiency, measured in two of the test orchards, were positively correlated with distance from the pollen source.