A lectin from fruiting bodies of Lactarius rufus (Scop.: Fr.)Fr. has been purified by affinity chromatography on copolymer of polyvinyl alcohol with a blood group B specific substance. The lectin gives a single band at disk-electrophoresis in acidic (pH 4.3) and alkaline (pH 8.6) buffer systems. Under electrophoresis in 10-20% SDS-PAGE, the lectin consists of identical subunits with molecular weight 17 +/- 1 kDa. Molecular weight of the lectin is 98 kDa according to gel-chromatography on Tojopearl HW-55. It is supposed that the lectin contains six subunits. The lectin is quite enough stable in pH 4.0-10.0, its activity does not depend upon bivalent metal ions. When heating the lectin solution to 65 degrees C it lost more than 85% of its activity. The lectin agglutinates human etrythrocytes without any marked group specificity, it agglutinates 2-4 times worse rabbit erythrocytes, very weakly crucian erythrocytes and does not agglutinate sheep erythrocytes. Mono- and disaccharides are not inhibitors of the lectin activity, while alpha-phenyl-N-acethyl-D-glucosaminopyranosid (0.08 mM) and 4-nitrophenyl-beta-D-glucosamin are the best inhibitors of its activity. Among glycoproteins the best inhibitors of the lectin activity are: group-specific substances from human blood erythrocytes, asialosubmaxillary bovine mucin, human and bovine thyroglobulin and more weak inhibitors are fetuin, transferrin and human Ig G.