Hyperglycemia and hypoxia synergistically retard diabetic wound healing. We investigated the direct effect of hyperbaric and normobaric hyperoxia on skin fibroblasts cultured in a high-glucose medium. Detroit 551 human dermal fibroblasts cultured in Dulbecco's modified Eagle's medium containing d-glucose had reduced cell survival compared with cells grown in normal glucose medium; survival was 27.5+/-3.8% lower in 25 mM glucose and 30.6+/-3.7% lower in 50 mM glucose. Cell survival decreased because of inhibition of cell proliferation and enhanced cell death. Daily hyperbaric oxygen therapy at 2.5 atmosphere absolute for 90 minutes on 3 consecutive days reduced cell proliferation and increased cell death in normal cultured fibroblasts. Hyperbaric oxygen therapy and high-glucose medium had a synergistic effect and reduced survival by 37.6+/-4.4% (25 mM glucose) and 39.6+/-5.1% (50 mM glucose). The effects of hyperbaric oxygen and high-glucose medium were associated with overproduction of reactive oxygen species. Our results suggest that direct exposure of skin fibroblasts to hyperbaric oxygen affects cell growth and superimposes the toxic effect of high glucose. This cytotoxicity may be related to the production of reactive oxygen species in the fibroblasts.