1. Samples of normal skin from four patients, post-burn hypertrophic scar from five patients and post-burn mature scar from six patients were analysed for hydroxyproline, water and uronic acid and extracted with guanidinium chloride to yield the proteoglycan pool. A large chondroitin sulphate proteoglycan and biglycan were purified from one hypertrophic scar biopsy and decorin from a normal skin biopsy, by ion-exchange chromatography, gel-filtration and hydrophobic interaction chromatography. These purified proteoglycans were used in an inhibition ELISA assay to estimate the quantities of each in the tissue samples. 2. Samples of post-burn hypertrophic scar had on average 30% less hydroxyproline, 12% more water and 2.4 times as much uronic acid as normal skin. These differences were all statistically significant, whereas the small differences between mature scars and normal skin were not. The content of decorin in hypertrophic scars was only 25% of that in normal skin whereas the large chondroitin sulphate proteoglycan and biglycan were each about 6-fold higher. The mature scars had slightly elevated levels of large chondroitin sulphate proteoglycan and biglycan and a reduced content of decorin compared with normal skin but these differences were not statistically significant. 3. The results suggest that aberrant proteoglycan metabolism is a significant factor contributing to the altered physical properties of hypertrophic scars and that maturation of post-burn scars is dependent on a return of the relative proportions and concentrations of proteoglycans to those characteristic of normal dermis.