Lectins associated with the bacterial cell surface of Rhizobium lupini strain LL13 were evidenced by erythrocyte agglutination, by aggregation of neoglycoprotein coated beads and by spectrofluorimetry using fluoresceinylated neoglycoproteins. At pH 5.0, a specific binding of the fluorescein-labelled neoglycoprotein bearing alpha-L-fucose was observed. The binding of this labelled neoglycoprotein is a saturable phenomenon and is inhibited by the same unlabelled neoglycoprotein. Extracts of R lupini obtained by disrupting a bacterial pellet through a French press were stabilized at pH 5.6 by gel filtration and purified to homogeneity by affinity chromatography on Agarose A4 substituted with alpha-L-fucose. A protein with a M(r) approximately 19,000 was specifically eluted from this affinity column with L-fucose. Isoelectric focusing of this sample yielded a single band with pI near 6.7. This protein specifically aggregated L-Fuc-BSA-coated microspheres. The results obtained in the present study indicate that we have purified from Rhizobium lupini strain LL13, a L-fucose binding protein as a lectin.