1Silk fibroin samples obtained by extraction of silk fibre with boiling, Na2CO3solution for different intervals of time were examined in 6M guanidine hydrochloride solution by gel filtration on agarose.2All the samples studied were heterogeneous. The weight‐average molecular weight of the samples estimated by gel filtration method was lower than that obtained by the Archibald ultracentrifuge method in 0.1 M KNO3solution.3This discrepancy was observed to be due to the dissociating effect of 6 M guanidine hydrochloride.4Sodium dodecyl sulfate and β‐mercaptoethanol also caused dissociation.5The thermal degradation of silk fibroin in Na2CO3solution followed a first order reaction kinetics.6Electrophoresis of the fibroins on polyacrylamide gels could not be performed since the protein remained at the top of the gel either due to precipitation of the protein or because of interaction with the gel. The experiments with buffer containing 6 M urea or 0.1% SDS also fa