n-Octyl-beta-D-thioglucopyranoside (octylthioglucoside), a new nonionic detergent, was synthesized. Properties of this detergent and its applicability to membrane biochemistry were investigated. The critical micelle concentration of this detergent was determined to be 9 mM. Membrane proteins of Escherichia coli were effectively solubilized with octylthioglucoside at 25-35 mM. The solubilizing power was equivalent to that of n-octyl-beta-D-glucopyranoside (octylglucoside). Reconstitution of the melibiose carrier into liposomes was performed by the detergent dilution procedure. It was found that the concentration range of octylthioglucoside for successful reconstitution (45-70 mM) was considerably wider than that of octylglucoside (43-46 mM), thus giving more reproducible results. Octylthioglucoside is more stable than octylglucoside. Furthermore, the former is synthesized with high yield at low cost whereas the latter is very expensive. Thus, we conclude that octylthioglucose is superior to octylglucoside, and is very useful in membrane biochemistry.