Although protein molecular weight markers are among the most commonly used reagents in molecular biology laboratories, simple and inexpensive means to produce such markers are lacking. We have therefore designed and prepared recombinant proteins of defined molecular weights from 10 to 150 kDa that migrate appropriately on SDS-PAGE gel. In addition to detection by Coomassie or silver staining, each protein contains an IgG binding domain that allows detection on Western blots without specific second antibodies.