Gel filtration has been applied to muscle proteins in the presence of the detergent sodium dodecyl sulphate (SDS). This detergent not only solubilizes a variety of proteins but also increases their hydrodynamic volumes, which is a disadvantage for the process of gel filtration. Nevertheless, appropriate choice of gel type, in this case Sephacryl S-400 Superfine, and optimal elution conditions make SDS gel filtration a useful tool in the separation of heterogeneous protein mixtures in the molecular weight range of 20,000–200,000.