Together with Allan Maxam, Gilbert developed a new DNA sequencing method, Maxam–Gilbert sequencing, using chemical methods developed by Andrei Mirzabekov. His approach to the first synthesis of insulin via recombinant DNA lost out to Genentech's approach which used genes built up from the nucleotides rather than from natural sources. Gilbert's effort was hampered by a temporary moratorium on recombinant DNA work in Cambridge, Massachusetts, forcing his group to move their work to an English biological weapons site.