In an effort to investigate the significance of platelet aggregation on early wound healing, the inhibitory effects of an antiplatelet drug (dipyridamole) on tensile wound strength was assessed. The breaking strength of the dorsal incisional wounds in Donryu rats both with and without the administration of dipyridamole was measured. In experiment I, the intraperitoneal administration of dipyridamole (100 mg/kg/day, Group A; 50 mg/kg/day, Group B) and saline (3 ml/day; Group C) was performed during the periods between the day of incision and the excision of the healing wound specimen in a 2.0-cm width on the third and seventh postoperative days (POD). The wound breaking strength was 229 +/- 44, 256 +/- 39, and 352 +/- 38 g/cm2 on POD 3 and 477 +/- 67, 578 +/- 60, and 764 +/- 31.9 g/cm2 on POD 7, in Groups A, B, and C, respectively. In experiment II, we performed the intraperitoneal administration of either dipyridamole (100 mg/kg) or 3 ml of saline as a control just before incision (Group a) as well as at 4 hr (Group b), and 12 hr (Group c) after incision, and the percentages of tensile strength compared with the control were 72 +/- 8, 89 +/- 13, and 103 +/- 23% in Groups a, b, and c, respectively. The administration of dipyridamole significantly inhibited the wound healing and, therefore, platelet aggregation would appear to play an important role in the early phase of wound healing.