Role of phenytoin in healing of large abscess cavities. The promotion of healing of large abscess cavities attained with topical phenytoin was evaluated in controlled studies of clinical and experimental wounds. In the clinical abscess cavities, phenytoin application in 20 patients compared with conventional treatment in 20 patients resulted in earlier separation of slough, decrease in oedema, control of pain and overall enhanced healing. The mean(s.d.) rate of reduction of wound area was 2.02(0.48) cm2/day in the phenytoin group versus 1.58(0.51) cm2/day in controls (P less than 0.05) on day 10, and 1.8(0.32) cm2/day versus 1.19(0.21) cm2/day (P less than 0.01) on day 20. The mean volume reduction rates at both the 10th and 20th day were 0.48(0.01) cm3/day for phenytoin versus 0.32(0.04) cm3/day for controls; (P less than 0.005). By day 20, 17 of the patients treated with phenytoin were rated as having healed completely, compared with only one of the controls. In a standardized guinea-pig model of the clinical abscess cavity, which included inoculation of the wound with Bacillus proteus and Klebsiella pneumoniae, an enhanced healing rate was also observed (at 7 days 0.40(0.05) cm2/day with phenytoin versus 0.21(0.08) cm2/day in controls; P less than 0.005). All eight of the animals treated with phenytoin healed by day 21, compared with one of the eight controls. Biopsies of wounds treated with phenytoin showed less inflammation, no necrosis, and enhanced neovascularization, collagen deposition and fibroblast proliferation compared to controls. Bacterial colonies also decreased more rapidly with the use of phenytoin. 