AbstractA previous observation by Nochumsonet al.[7], showing that agarose after reduction or abolition of its supercoiled structure by hydroxyethylation (SeaPrep 15/45), exhibits a molecular sieving effect similar to polyacrylamide in sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) was confirmed and quantitated by Ferguson plot analysis in PAGE. SeaPrep 15/45 exhibits an effective fiber radius of 0.8 nm, as compared to 23.8 nm for native agarose and 0.4 nm for 2 % crosslinked polyacrylamide. Its effective pore size (estimated as\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {{\rm K}_{{\rm R polyacrylamide}} } /\sqrt {{\rm K}_{{\rm R agarose}} } $\end{document}) is 0.88 times that of polyacrylamide 2% crosslinked with N,N'‐methylene bisacrylamide (Bis). Although this is not a practical result as yet, due to the low melting temperature and poor gel strength of SeaPrep 15/45, it does sound the death knell for the use of crosslinked polyacrylamide in macromolecular separations, by demonstrating that a linear polymer capable of forming a gel on mere cooling is equivalent to the product of a laborious and relatively irreproducible free radical polymerization. It remains to find a linear polymer with higher melting point and better mechanical strength and adherence to glass walls than SeaPrep 15/45 to make crosslinked polyacrylamide obs