Objective; The changes of mast cell numbers in different zones of acute random pattern skin flaps after the flap construction were investigated in rats. Material and methods: A caudally based dorsal skin flaps (McFarlene's flap) measuring 3x9cm were raised and flaps were divided into three zones, zone-1 represented the proximal well-perfused area, zone-2 represented the intermediate-transition zone and, finally zone-3 represented the distal-ischemic zone. Skin biopsies were obtained from all three zones at 10 1 minute in group I, at 4l hour in group 2, at 811 hour in group3 , at 12 th hour in group 4, at 24" hour in group 5 and at 8" day in group 6 after the flap elevation. Additionally normal skin biopsies were taken from ventral skin of each animal as a control. All specimens were stained with toluidine blue and mast cell numbers in biopsies were counted. Results; Our results clearly show that at least a two-fold increase in number of MC occurs as early as 10 minutes after flap elevation. This high levels remains constant to 24th hours of flap construction. When we compared the proximal and distal zones of flap, we have found that MC numbers progressively increased towards to the distal zones. Conclusions; A positive correlation exists between MC numbers and tissue ischemia, although the exact mechanisms is not clearly understood how mast cells act in tissue hypoxia.