The genetic population structure inBdallophyton bambusarum, an endoparasite, was studied in ten subpopulations from a subdeciduous tropical forest in Veracruz Mexico. The sample was analyzed using seven polymorphic loci in cellulose acetate electrophoresis. Isozyme data indicated that the subpopulations ofB. bambusarum contained high genetic variability (Hep = 0.452 ± 0.045, S.E.). Our analysis suggests that almost each inflorescence ofB. bambusarum is an individual. The subpopulations studied were genetically similar (average Nei's genetic identity 0.941 ± 0.051 and F st values 0.097 ± 0.026), suggesting that genetic differentiation among subpopulations was small. Direct estimates of effective population size was derived from observations of three fluorescent dyes, and from the genetic neighborhood area derived from these data. The neighborhood area, multiplied by the total density of individuals, gave an Ne = 124.84 plants, and when corrected to consider the proportion of males and females gave an Ne = 118.59 individuals. An indirect estimate of Nm was obtained from the F st values (mean Nm=2.037), giving an indirect estimate of the effective population size Nb = 12.8 individuals. Both values are relatively high when compared to other plant studies. The gene flow and/or effective populations size of the studied subpopulations ofB. bambusarum are believed to be large enough to prevent differentiation among subpopulations due to genetic drift.