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Two endemic species of wild cotton, Gossypium sturtianum and G. australe, occur near the eastern Australian cotton growing regions. These species can be crossed artificially with cotton (G. hirsutum) and experimental doubling the chromosome number of the hybrid overcomes its sterility. It is therefore remotely possible that the same processes might occur in nature, and transgenes from genetically engineered cultivars might leak into natural populations. To evaluate the risk further, we compared the distribution of the wild species with the Australian cotton growing area, and examined their natural breeding system. A survey of herbarium records showed that only a small portion of the distribution of these wild species approaches the cropping area. Isozyme variation in samples from two populations each of G. sturtianum and G. australe gave estimates of outcrossing of about 4% and 40% respectively. The major barriers to gene escape into the wild species via pollen is the remoteness of most of their populations and the unlikelihood and the sterility of interspecific hybridization. Predominant self-pollination in G. sturtianum thus forms an additional barrier, and reduces still further the risk of their escape from the crop into wild populations.