Pieces of the integument cut off from the hind tibiae of the freshly moulted adult cockroaches were cultivated in vitro. The epidermis reacted to the application of 2 x 10-5 mol l-1 ecdysterone by an apolysis. If thereafter the hormone concentration stayed above a concentration of 2 x 10-7 mol l-1 only epicuticle and exocuticle were deposited. However, when the hormone concentration was reduced below a critical threshold, that was possibly between 2x10-7 and 2x10-8 mol l-1, a composite procuticle with exocuticle and endocuticle was deposited. Neither application of dibutyryl-cAMP to the culture medium, nor co-cultivation of the ventral nerve cord of a freshly moulted adult had distinct effects. Obviously, bursicon was not necessary for deposition of the endocuticle; instead, Riddiford´s sequential cascade model was fulfilled. The cuticle also developed the typical patterns of sclerotization independently of the application of dibutyryl-cAMP and the co-cultivation of a nerve cord.