This invention provides a method for solubilizing and recovering in bioactive form, a target polypeptide or protein that has been expressed from a host organism in insoluble form. The polypeptide is isolated from the host organism by standard procedures including disrupting the host cell to produce a lysate and recovering the precipitate from the lysate. The precipitate containing the polypeptide is solubilized in a non-denaturant and detergent free non-buffered solubilization solution containing sodium hydroxide between 8 and 10 mM, mannitol between 2 and 5 mM and lactose between 1 and 2 mM. The resultant solubilization preparation contains a biologically active target polypeptide between 1 and 4 mg per ml of solubilization solution. The solubilized polypeptide obtained in this particular manner constitutes the object of the invention. The bioactive solubilized polypeptide is then transferred into an appropriate buffered solution of the desired pH and purified following conventional chromatographic procedures.