Effective solubilization of the major platelet membrane component, the glycoprotein IIb.IIIa complex, can be achieved with 8 M urea. By avoiding nonionic detergents in the separation medium it is possible to obtain clear immunoblot patterns without interference from the isoelectric focusing matrix. Upon running on a pH 4.25-5.25 immobilized pH gradient, immunoreactive bands corresponding to the nonreduced IIb.IIIa complex stain between pH 4.5 and 5.0. The method appears of significant potential utility in evaluating glycoprotein IIb.IIIa polymorphisms under different clinical conditions.