AIM: To obtain some insight into the extracellular matrix in the placenta, changes in the composition of collagens during placental development were investigated. METHODS: Collagen was extracted from placentas (group 1, 25-30 weeks, n = 21; group 2, 31-36 weeks, n = 32; and group 3, 37-41 weeks of gestation, n = 40) and the relative concentrations of various collagens were evaluated by SDS-PAGE. RESULTS: The ratio of the intensity of the alpha 1 (III) band to that of alpha 1 (I) chain collagen in group 3 placentas were lower than those in group 1 placentas. In contrast, the ratio of the intensity of the alpha 1 (V) band to that of alpha 1 (I) chain collagen in group 3 placentas were higher than those in group 1 and group 2 placentas. CONCLUSIONS: These results suggest that type V collagen might play an important role in the function of the placenta and that an increased relative concentration of type V collagen might be closely associated with the development and ageing of the placenta.