A sequence of adjacent samples of beef 1. dorsi muscle were alternately exposed either to conventional heating for periods of 0-70min at temperatures between 45" and 90°C or to microwaves at a frequency of 2450 MHz for periods of 0-10 sec at power levels between 131 and 1050 W. Protein denaturation was assessed by measuring nitrogen distribution between sarcoplasmic and crude myofibrillar fractions and by electrophoresis ; and concomitant superficial changes in free water and plasticity measured.The attainment of' a given temperature by microwave energy was associated with less detrimental change than when achieved by conventional heating; but this could be attributed merely to further progression of the same type of effects due to the time necessitated with the latter procedure and not to any qualitative d.ifference. The findings suggest that microwave heating might permit microbial inactivation in meat products with minimum loss of organoleptic quality. It is also suggested that the observed initial resistance of myoglobin to heat denaturation and its subsequent loss of electrophoretic mobility between 75" and 88°C could be developed as an index of the temperature attained by meat products.