Conservation of genetic variation in a species which occurs as a few disjunct populations poses particular problems related to both the separation of those populations and their size. Lobelia urens is rare in Britain and occurs in only six widely separated populations. The distribution of genetic variation within and among these populations was examined using enzyme electrophoresis. The results showed that much of the variation was held among populations (G(ST) = 0.265) and that gene flow among populations was low. The populations therefore require conservation as independent units. No link was found between geographical distance and genetic distance, adding weight to the theory that the British populations were established independently. Evidence was found that the smaller, unmanaged, populations contained less variation, although all had passed through a series of bottlenecks during the past 50 years. As surrounding vegetation becomes more dense, fewer individuals contribute to variation in population size and it is suggested that periodic disturbance should be used as a management tool in order to release variation accumulated in the seed bank and so prevent depletion of genetic diversity.