Summary The ultrastructure of annulate lamellae of the jejunal absorptive cells in control and 21 d starved rats was investigated. Annulate lamellae were only rarely encountered in the jejunal absorptive cells of control rats, and then frequently in small stacks continuous with the rough-surfaced endoplasmic reticulum. In contrast, there was a relatively frequent incidence of annulate lamellae in the jejunal absorptive cells of 21 d starved rats, and larger stacks of annulate lamellae were also observed in spite of marked ultrastructural changes of these cells. The annulate lamellae were also continuous with the rough-surfaced endoplasmic reticulum, which was degenerating. The degenerative process of the absorptive cells following starvation might be related to the origin and function of the annulate lamellae.