The blood flow in 37 free flaps used for intraoral reconstruction was measured by laser Doppler flowmetry before and after elevation of the flap during surgery, immediately after the completion of reconstruction and on the 1st, 2nd and 3rd postoperative days (1 POD, 2 POD, 3 POD). Although the blood flow decreased temporarily after the flap elevation, it began to increase immediately after reconstruction and continued a gradual increase thereafter, reaching a peak on 2 POD. The flap survived in all cases where the blood flow on 3 POD was equal to or greater than that before flap elevation. Total necrosis of the flap occurred in one patient, and partial necrosis in another. In both patients, abnormal laser flow-metric measurements preceded the manifestation of the clinical signs. Using laser Doppler flowmetry to monitor free flaps both during surgery and for three days thereafter is thus a useful way of determining their viability.