When cultivated within a matrix made of reconstituted collagen fibers, fibroblasts derived from skin, tendon, vena cava, and aorta of a normal (N) calf retract the lattice. This effect progresses with time and is related to the density of the cells included in the lattice. Under similar conditions, fibroblasts derived from the skin of 2 dermatosparactic (D) calves do not contract the lattice. Fibroblasts from D tendon and cells from D vena cava and aorta contract the lattice at the same rate and to the same extent as do their normal counterparts. In the lattice, N skin fibroblasts are elongated along the collagen fibers while D skin fibroblasts remain round and develop little cell processes. N skin fibroblasts do not multiply in the lattice while D skin fibroblasts increase in number by a factor of 3 in 5 days. The addition of N skin fibroblasts, in an amount insufficient to retract the lattice, to D skin fibroblasts does not correct their defective capacity. It is suggested that the disturbed relationship between the D skin fibroblasts and collagen fibers is responsible for the lack of architectural organization of the bundles of collagen polymers in the D skin.