Villitis of unknown etiology (VUE) is a common placental lesion and complement-fixing immune complexes is one of the mechanisms proposed for its development. We examined 16 placentas with VUE and 16 without VUE by immunofluorescence in order to compare the distribution and amount of C1q, C3d, IgG and IgM in the chorionic villi between the two groups. We found both in cases with and without VUE a distribution Or the complement components and immunoglobulins similar to that described in normal placentas. The amount of deposit was also not significantly different in the two groups. Only the inflamed villi showed an abnormal distribution of C1q which was present diffusely in the stroma of these villi.202129134