The AutoSpot SL performs the most critical step, reliable, precise delivery of sub-µl volumes of reactive derivatives to the array positions on up to four cellulose membranes. Several hundred peptides are thus assembled in successive synthesis cycles on a support of microtiter plate size. An optimized chemistry has been established to provide quality peptide sets at low cost on a routine basis. They remain bound to the membrane and can be compared in a single assay for their biological activity.