We have previously shown that the expression of collagenase mRNA and activity are suppressed in fibroblasts derived from postburn hypertrophic scar. Although it is known that differential synthesis of collagen and collagenase in postburn hypertrophic scar is one of the main reasons for the excessive accumulation of collagen, it is not clear why the expression of collagenase in hypertrophic scar fibroblasts is suppressed relative to that in normal fibroblasts. In this study, we hypothesized that dermal fibroblasts from deeper layers of skin, which normally migrate toward the wound site, have a different capacity to express key extracellular matrix proteins such as collagenase and types I and III procollagen. To test this hypothesis, we established four different pairs of hypertrophic and site-matched normal cell strains from four different patients with postburn hypertrophic scarring. In another set of experiments, ten different cell strains from two normal human skin samples that were horizontally sectioned into five different layers (layers 1-5 correspond to upper to deeper layers, respectively) were established in culture. Cells at the same passages were harvested, total RNA was extracted, and Northern analysis was conducted to determine the level of collagenase and types I and III procollagen mRNA expression in each cell strain. The results of Northern blot analysis showed two transcripts each for the pro alpha1(I) collagen chain (5.8 and 4.8 kb) and for the pro alpha1(III) collagen chain (5.4 and 4.8 kb) in all cell strains examined. The intensity of the pro alpha1(I) chain of type I procollagen mRNA varied, ranging from 50.8 to 137.1 and 44.4 to 131.5 densitometry units among either normal or hypertrophic scar cells examined, respectively. Similarly, the relative quantity of type III procollagen transcript also varied, ranging from 10.4 to 91.1 and 28.7 to 116.1 among normal and hypertrophic scar cells, respectively. When five different skin layers from each tissue sample were evaluated for functional cell heterogeneity, the results showed a marked variation in expression of mRNA for type I and III procollagen. Although the level of collagenase mRNA also varied among different cell strains examined, the expression of collagenase mRNA was lower in fibroblasts derived from deeper layers of each skin sample. In conclusion, cells from different layers of normal skin samples are heterogeneous in their constitutive expression of some key extracellular matrix components such as collagenase and types I and III procollagen.