A technique for strain‐level identification within a Rhizobium biovar is described, based on automated sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE) of35S‐labelled proteins, offering substantial improvements on existing SDS‐PAGE methods particularly in the areas of standardization of electrophoresis conditions and rapidity of positive identification. Gels were analysed with a β‐scanner, the beta particle emission data being directly relayed to an IBM PC/AT computer for subsequent manipulation. Analysis of the total protein profiles obtained by this method revealed regions of variability between strains of R. leguminosarum bv. trifolii. Automated comparison of these regions enabled identification of strains. The method was successfully used for identifying root nodule isolates obtained from competition studies between known pairs of R. leguminosarum bv. trifolii strains inoculated onto Trif
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