Abstract A fourth molecular form of α-galactosidase has been discovered in leaves of Cucurbita pepo and a 6-fold purification achieved by ammonium sulphate precipitation and ion exchange chromatography. The enzyme designated L IV has the unique property among α-galactosidases of possessing an alkaline pH optimum at 7.5 with p-nitrophenyl- α-D-galactopyranoside (PNPG) or stachyose as substrates. Raffinose hydrolysis was optimal at pH 6.5–7.0. A K m-value of 0.60 mM for PNPG hydrolysis was obtained. In immature importing leaves L IV activity was about 3-fold higher than the total acid α-galactosidase activity. Through the transition phase, during which the leaf changes from an importing to an exporting organ, a 6-fold decline in L IV activity occured. In mature leaves L IV activity was about 60% of the total acid α-galactosidase activity. It is suggested that L IV may play a major role in the hydrolysis of stachyose imported into immature leaves.