Separation of a series of poly(ethylene glycols) (PEGs) by sodium dodecyl sulfate-poly(acrylamide) gel electrophoresis (SDS-PACE) is investigated. Unlike for proteins, preincubation with SDS is not a prerequisite for the electrophoretic movement of PEGs; nevertheless, presence of SDS in the running buffer is essential. The bands are detected by staining with Dragendorff's reagent (iodobismuthate) which forms an insoluble complex with PEG. Exclusion of a stacking gel above the separatory gel better resolves the low molecular weight PEGs (<10000), but high molecular weight yield well separated bands by both methods. To elucidate the mode of transport, PEGs samples were electrophoresed alongside marker proteins of comparable molecular weight and detected by a two step staining process involving Dragendroff's reagent for the former and coomassie blue for the latter. PEGs moved along with proteins of twice the molecular weight. The possibility of PEG chains migrating with dodecyl sulfate ion (DS-) cloud is discussed.