Any necrosis after reconstruction of the modified radical mastectomy defect using a superior epigastric based unipedicled lower transverse rectus abdominis myocutaneous flap should be unusual. Identification of the marginal flap at risk for this complication is important as this would permit immediate microvascular augmentation to enhance total survival. The dilemma, then, is how to define which flaps would benefit. We believe this is possible using laser Doppler flowmetry as a continuous, noninvasive, objective monitor of flap perfusion. Flow characteristics have been obtained in 16 consecutive transverse rectus abdominis myocutaneous flaps using the laser Doppler, where 2 were shown to have been in jeopardy for major flap loss. After appropriate microanastomoses as indicated, all flaps totally survived as predicted.