A single Mendelian locus has been described (Devine, 1984) that condi-tions ineffective vs. effective nodulation response upon inoculation of soy-bean lines withRhizobium fredii (Scholla and Elkan, 1984). A formal gene sym-bol has not been assigned to this locus; for convenience, we will refer to it here as Rj?. In a breeding program with a long-term goal of developing adapted cultivars with an effective response toimprovedR. fredii strains, it might be more efficient to select for the effective nodulation response indirectly (via a tightly linked genetic marker) than by screening lines for nodulation response directly. In this study, we tested 5 loci for linkage with the locus conditioning effective nodulation.