Ricin B chain has been isolated from highly purified RCA60. B chain is the component of ricin which binds surface carbohydrate receptors and facilitates the transport of ricin into the cell. Although our ricin B chain has a substantially lower toxicity than native ricin in both cell culture test systems and cell-free protein synthesis assays, essentially all of the galactose/ N-acetylgalactosamine binding activity is retained. Ricin B chain is a glycoprotein with an isoelectric point of about pH 4.8 and migrates as a single band on SDS-PAGE under reducing conditions with a molecular weight of about 32,000.