Abstract 1. 1. Treatment of cellulose acetate gel strips by boron trifluoride in methanol has been shown previously to produce a material suitable for isoelectric focussing. Further observations are reported here on the changes in the strips induced by the reagent. It has shown by conventional protein electrophoresis, for example, that not only is the degree of electroendosmosis reduced, but also that other properties are altered. 2. 2. Minor modifications are introduced for the general isoelectric focussing method including improved electrode solutions. 3. 3. Isoenzyme detection following isoelectric focussing of serum proteins is discussed in the light of experience gained using alkaline phosphatase and lactate dehydrogenase as examples.