Until recently, the muscle meat protein content of comminuted and heated meat products could be estimated by subtracting the connective tissue content from the total protein content. Both contents can be fairly well determined. Today, however, the potential use of non-meat proteins makes it very difficult to estimate the muscle protein content of the meat product. This is one of the reasons for which extensive studies were done to develop a direct method for determination of the muscle meat content. An accurate parameter for this muscle meat is not available. In the present investigations, the proteins of meat of various animals (cow, pig, chicken and horse) were studied by SDS polyacrylamide gel electrophoresis. The thermo stability (heating for 30 minutes at temperatures ranging from 50 degrees C- 120 degrees C) of the meat proteins was also studied. The pherograms of the SDS-extracts of these kinds of meats appeared to be very similar. The various myofibrillar proteins were plainly perceptible in every case. Particularly actin was found to be resistant to a heating procedure for 30 minutes at 90 degrees C (and even higher). As regards the analytical problems relating to the estimation of the muscle meat content, actin would appear to offer good perspectives.