AbstractProtein molecular weight standards labeled with different fluorochromes were tested for their usefulness in following the protein transfer from sodium dodecyl sulfate‐polyacrylamide gels to nitrocellulose and for electro‐elution of proteins from polyacrylamide gels. Dichlorotriazynylaminofluorescein labeled proteins appear to be useful for both purposes as they are stable, their detection sensitivity was high (about 10 ng of protein on nitrocellulose) and the coupling of the fluorochrome did not appreciably change the molecular weight of any protein examined. On the other hand, proteins labeled with tetramethylrhodamine isothiocyanate, or its heterocyclic derivative, were of limited usefulness as standards. Labeled proteins of molecular weight below 20 kDa formed diffuse bands on gels. Therefore, these particular fluorescent protein standards appear to be useful in following the elution from gels, or as references on nitrocellulose, only for proteins larger than 20–2