The B 4 isolectin from Griffonia simplicifolia is of great utility as a reagent for the identification of α-d-galactopyranosyl end groups. Its separation from isolectins containing A subunits has been greatly improved by a simple, rapid procedure using a column of N-acetylgalactosamine coupled to vinyl sulfone-activated Sepharose 4B to selectively retain the A subunit-containing isolectins. The procedure has the advantages over previous affinity procedures of speed (the isolation of B 4 isolectin can be achieved in one day), simplicity, and high degree of resolution of the B 4 isolectin.