Banded fibrils previously only described under stratified epithelia (9) are described in the subepithelial zone of simple epithelia in the uterus in adult, spayed and 30-month mice. The characteristic fibril is about 4000 Å in length and has a cross-banding pattern which is symmetrical about its midpoint. Each end of the fibril is attached to basal lamina material. This is most clearly seen in spayed animals where masses of basal lamina material have become detached from the epithelium. The possibility that these structures represent a naturally occurring dimeric aggregation of tropocollagen is discussed. © 1969 Academic Press, Inc.