We describe a simple technique for reacting CK isoenzymes with a substrate in gelatin to make them visible after they have been separated by cellulose acetate electrophoresis. The electrophoresed strip requires only 5 min of contact with the substrate in gelatin and about 12 min of drying in an oven at 55 degrees C. The developed isoenzyme bands are discrete, intense, and rectangular in shape. The technique has a sensitivity of 2 to 5 U/liter, and results for isoenzyme MB can be reported about 30 min from the time a specimen is received.