AIM: To provide some insight into the aetiology of spontaneous abortion, the contents of type V collagen was investigated in human decidual tissues in spontaneous abortion and normal pregnancy. METHODS: Collagens were extracted from decidual tissues in spontaneous abortion (n = 19) and normal pregnancy (n = 25). The different types of collagen alpha chains were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), stained with Coomassie brilliant blue, and measured by densitometry. The relative amounts of the alpha 1 (III) and alpha 1 (V) chains were calculated by dividing the band intensities of the alpha 1 (III) and alpha 1 (V) chains by that of the alpha 1 (I) chain. RESULTS: The ratio of the alpha 1 (V) chain to that of the alpha 1 (I) chain in decidual tissues in spontaneous abortion was significantly lower than that found in normal pregnancy (p < 0.05). CONCLUSIONS: These results suggest that type V collagen might play an important role in the maintenance of pregnancy and that decreased expression of this collagen could be associated with spontaneous abortion.