pollen pool heterogeneity, which violates an assumption of the mixed-mating model, is one of the major problems facing population geneticists concerned with measuring plant mating systems. in the present study, isozyme markers were used to examine pollen pool heterogeneity in two natural populations of jack pine, pinus banksiana lamb.,in northwestern ontario, canada. population multilocus estimates of outcrossing rate ranged from 0.829 to 0.952 and differed significantly between populations. singletree outcrossing rates were found to be homogeneous among trees in both populations. computer simulation studies shoved that the consanguineous mating pollen pool was a potentially important component of the pollen pool, capable of biasing population outcrossing estimates downward. in contrast, random heterogeneity of the pollen pool was found to have no effect on population estimates of outcrossing rates. pollen pool heterogeneity existed in these two natural populations. however, it appeared to be random in nature and therefore did not affect the population outcrossing estimates.