Based on a continuing need to provide a more rapid response to requests for thawed fresh frozen plasma, the authors evaluated plasma thawing with the use of a microwave oven and compared it with conventional 37 degrees C waterbath thawing methods. Their results indicate that microwave-thawed plasma contains precipitated denatured protein (mainly albumin and fibrinogen) and that there is a significant reduction of coagulation Factors IX, X, XI, and fibrinogen compared with fresh plasma. They also measured levels of di-ethyl hexyl phthalate after microwave thawing and found its rate of accumulation similar to that of the 37 degrees C waterbath. More importantly, fundamental principles of microwave heating preclude uniform temperatures being maintained throughout the thawing of plasma; hence, the denaturation of plasma proteins is expected to occur under even low heating conditions.