Racospermaauriculiforme(Cunn. ex Benth.) Pedley andRacospermamangium(Willd.) Pedley are two fast-growing multipurpose leguminous species that have great potential for reforestation in the subhumid and humid tropics. The level and distribution of genetic variability were evaluated among and within 13 populations of each species at 18 loci encoding 10 enzymes, using starch gel electrophoresis. At the population level, the mean number of alleles per locus, the mean percentage of polymorphic loci, and mean expected heterozygosity were, respectively, 1.9, 52.1%, and 0.122 forR.auriculiforme, and 1.5, 24.3%, and 0.064 forR.mangium. Therefore,R.mangiumappeared genetically depauperate compared withR.auriculiforme. The proportion of the total genetic diversity that resided among populations inR.auriculiforme(18%) was twice that inR.mangium(9%). No linear relationships were detected between genetic and geographic distances among populations. Cluster analysis of Nei's genetic distances and discriminant analysis did not show any significant geographic pattern of population differentiation forR.mangium. These same analyses revealed two distinct clusters of populations forR.auriculiforme, one in Queensland, Australia, and Papua New Guinea, and the other in the Northern Territory of Australia and Indonesia. For both taxa, seed of unknown origin of some introduced populations in Zaire and Congo could be identified. The genetic distance between the two species (D = 0.097) was, as expected, much larger than the average intraspecific genetic distance derived from comparisons of conspecific populations (D = 0.034 forR.auriculiformeandD = 0.007 forR.mangium). However, the amplitude of the interspecific genetic distance calculated is representative of divergence levels usually observed among subspecific taxa. Based on this, and the lower levels of genetic diversity found inR.mangium, it is suggested thatR.mangiumderived recently fromR.auriculiforme.