In the larvae of Boophilus decoloratus and B. microplus the integument is of 2 morphologically distinct types. The major part of the integument consists of sclero-tised cuticle. This type of cuticle is non-lammellate, and has relatively straight pore canals. The underlying hypodermis is flattened and exhibits little synthetic activity. The cuticle of the dorsal regions stains more intensely with lead and has wider pore canals than the remainder of the cuticle. In the intersegmental regions there is un-sclerotised cuticle. In this type there is an obvious separation of a lamellate endo-cuticle and non-lamellate exocuticle, and cuticular projections are present. Within the lamellae, microfibrils can be resolved and they exhibit a parabolic pattern. The pore canals are crescentic. The underlying hypodermis is cuboidal and appears to be more active than the hypodermis of the sclerotised cuticle. The epicuticle consists of a dense layer, a cuticulin line and a wax layer. The pore canals are connected to the cuticulin line by wax filaments. The cuticle of the adult ticks has a fibrous endocuticle and a smooth exocuticle. The epicuticle is similar to that found in the larvae. The fibrous endocuticle contains microfibrils that are arranged in parabolic patterns, except in the fully engorged adult where the pattern is disrupted. The underlying hypodermis consists of columnar epithelial cells. These have a short microvillar border and masses of ribosomal material. Secretory vesicles are found in the apical region, and some of these appear to be undergoing reverse pinocytosis. The cells are particularly active in the early stages of engorgement and become disorganised during the final stages of rapid engorgement.