Four forms of β-galactosidase were isolated and partially purified from the cotyledons of germinating seeds of Vigna radiata by ammonium sulphate fractionation and ion exchange chromatography through DEAE-cellulose and CM-cellulose columns. These multiple forms showed similar pH optima and temperature optima but differed from each other in Mr, ionic charge, kinetic parameters, activation energy and sensitivity towards heat, metal ions and certain chemical agents. From their Km values, p-nitrophenyl β-d-galactoside appeared to be a better substrate than o-nitrophenyl β-d-galactoside for two of these enzyme forms, whereas, the converse was found for the other two forms. © 1990.