Supplemental mass pollination (SMP) success rate in a mature Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seed orchard was studied with the aid of a unique electrophoretically detectable allozyme marker. Operational applications, and branch applications that were carried out one, two, or three times, were conducted during the orchard's maximal pollen release (i.e., the height of pollination). No significant increase in seed-yield traits (total number of seeds per cone, number of filled seeds per cone, and seed efficiency) was observed between wind-pollinated and SMP-treated (operational and one and multiple branch visits) cones. However, multiple branch visits (18%) showed significant increase in SMP success rate when compared with the operational visit (8%) or the one branch visit (9%) results. No significant increase in SMP success rate was obtained when the number of branch visits was increased from two (17.8%) to three (17.9%). It was concluded that operational SMP had the potential to improve the genetic value of the treated Douglas-fir crops even under high pollen load. The degree of improvement is dependent directly on SMP fertilization success and indirectly on the genetic value differential between the supplemented and the orchard's ambient pollen, the frequency of application, and the quality of the pollen applied (i.e., viability).