The healing rate of small experimental burns continuously treated topically with 96% O2and 75% relative humidity was followed for 25 days. Serial image photographic magnifications (tenfold throughout) of the wounds enabled precise measurements of their size by means of a polar planimeter. Healing rate was expressed as decreased percentile of wound size on a given day compared to the initial area. The mean percentages of healing ± SEM of the humidified O2treated wounds on postburn days 6, 11, and 16 were 31.25 ± 6.15, 82.09 ± 3.52, and 98.29 ± 1.46, respectively, and those for the control wounds were 7.08 ± 2.20, 47.68 ± 3.39, and 84.41 ± 1.38, respectively. Analysis of variance revealed highly significant differences in the healing rate between O2-humidity-treated and control wounds (p< 0.005). The results indicate that topical treatment with 96% O2and 75% relative humidity improved healing of experimental burns in guinea pigs.