Human dermal fibroblasts were cultured in a hydrated type I collagen lattice. When collagen fibers were arranged in one direction, fibroblasts were arranged in the same direction. Cell proliferation was markedly suppressed in the collagen lattice as compared with that on plastic, with growth being arrested after day 5. No differences in proliferation were observed between aligned cells and randomly oriented cells. Flow cytometry with DNA staining was performed to analyze each phase of the cell cycle of fibroblasts. Among the 10,000 cell population, S phase cells on day 2 of culture accounted for 43% on plastic but were markedly inhibited to 25% in the lattice. On day 4, S phase cells accounted for 33% on plastic but only for 10% in the lattice. These findings suggest that cell advancement to the S phase is markedly inhibited in the collagen lattice, resulting in accumulation of most of cells in the G0G1 phase. The present study clearly showed that culture in the collagen lattice allowed alignment of fibroblasts with a definite orientation as observed in vivo and produced a status resembling that in vivo in terms of proliferation and cell cycle phase composition.