To develop the use of electrophoretic lipopolysaccharide profiles for Bradyrhizobium strain identification, we studied the feasibility of using electrophoresis of whole legume nodule homogenates to obtain distinctive lipopolysaccharide profiles. The electrophoretic patterns were the same whether we used nodule extracts, bacteroids, or cultured bacteria as samples, and there was no evidence of changes in the ladder-like pattern during the nodulation process. To assess the reliability of using lipopolysaccharide profiling performed with individual nodules for studying the diversity and microdistribution of the rhizobia nodulating wild shrub legumes, we used a population of Adenocarpus foliolosus seedlings. We obtained 75 different profiles from the 147 nodules studied. There was no dominant profile in the sample, and a plant with different nodules generally produced different profiles. Electrophoresis of legume root nodules proved to be a fast and discriminating technique for determining the diversity of a bradyrhizobial population, although it did not allow the genetic relationships among the nodulating strains to be studied.