A dorsal skin flap chamber model was developed for analysis of the microvascular response to moderate intensity local thermal burns. Fluorescein isothiocyanate tagged 70,000 d dextran was introduced to visualize the extravasation and interstitial transport of macromolecules at the burn site. Contact burns 0.5 cm in diameter were affected by touching a thermostated metal rod onto the exposed epidermal side of the chamber preparation. All burns were of 5-second duration at temperatures between 55 degrees C and 70 degrees C. Postburn leakage of the fluorescein-labeled probed was monitored at numerous sites in the preparation on a fluorescent microscope equipped with a low-light-level intensified silicon intensified target video camera and recorded on tape for subsequent quantitative analysis. Selected scenes were digitized and subjected to a sequence of computer-image processing operations to extract quantitative information about the concentration distribution and net accumulation of dextran in the interstitial space as a function of postburn time. A diffusion model based on cylindrical geometry was fit to the concentration profile data at each site analyzed, and an apparent diffusion coefficient describing the interstitial transport process was determined. The interstitial transport increased with burn temperature up to a threshold of 70 degrees C, where other factors resulted in significant reduction in the loss of fluorescent macromolecule from the vasculature.