The effects of supplemental mass pollination (SMP) were studied in two Pinus sylvestris seed orchards differing in pollen production. Pollen was dusted over the whole tree during the period of peak female receptivity using a pressurized backpack sprayer. The success of SMP was assessed by means of allozyme markers. In the orchard with high pollen production, detectable differences in SMP success rate were found between clones, but the success rate was not influenced by the number of pollinations per day. The average estimated success rate of SMP was 19%. In the orchard with low pollen production, no significant differences in SMP success rate were found between years (22 versus 34%) or between clones. The SMP success rate in the low pollen production orchard varied between 14 and 69%.