The ultrastructure of striated ventromental plates and their relationship to other parts of the larval head capsule have been studied in two Chironominae species,Microtendipes pedellus(Degeer) andChironomus ripariusMeigen, by scanning electron microscopy and light microscopy, including observation of thin sections. In both species the inner surface of the striated plates has a complex microarchitecture and is closely associated with a cuticular structure termed the maxillary plate. It is suggested that the striated and associated maxillary plates play an important rr̂le in the process by which larvae of the Chironominae spin silk.