The relative percentage of type III to type I collagen, the ratio of alpha 1(I) to alpha 2(I) collagen chains and the ratio of dimers (beta-chains) to monomers (alpha-chains) in type I collagen have been measured in solubilized collagen fractions from keloids and hypertrophic scars aged about 1-7 years after burn. In tissue samples the content of crosslink with structure of pyridinoline were analyzed and expressed as mole of crosslink per mole of collagen. A comparison between hypertrophic and keloid scars has shown that the young (about 1 year) hypertrophic scars have higher ratios alpha 1(I)/alpha 2(I) and beta 11 + beta 12/alpha 1(I) + alpha 2(I). The increased proportion of beta-chains in the younger hypertrophic scars approximated to the same level as in normal skin within 7 years after lesion. There was no decrease in the ratio dimers/monomers of collagen type I with age of keloid scar tissue. The relative amount of collagen type III in young keloid scars was found decreased as compared to age-matched hypertrophic scars (13 +/- 3 and 17 +/- 7 respectively), but was similar in the older scars. The average pyridinoline crosslinks content per mole of collagen in keloids was 2 times as high as in hypertrophic scars. The data support the suggestion that general, as well as peculiar disturbances of collagen metabolism are involved in the development of keloids and hypertrophic scars.