The cement substance around the mouthparts of female ixodid ticks, Haemaphysalis spinigera , attached to a host (rabbit) consists of external cement forming a cone, with a quite substantial lateral extension into the more superficial skin layers, and internal cement. The internal cement, which is a continuation of the cement cone and which extends deeper into the skin, consists of a tapering tube surrounding the mouthparts, other than the palps which are flexed laterally outside the cone. The hypostomal teeth lock with corresponding impressions on the inner surface of the tube, while the outer surface of this tube takes the form of strand-like protrusions of cement extending between fibrils of the surrounding deep dermal tissue. The overall mass of cement in the host's skin may be as much as 0.042 mm2. Males show similar features but the wing-like extension of the cone and the strands from the tube in the skin are much reduced. Histochemical study, particularly of sulphydryl groups, indicates that the cement is mainly protein and is derived from the salivary glands from precursors in the (a) cells of type II alveoli and (c) cells of type III alveoli (external cement; cone and lateral wing-like extension) and in the (d) cells of type III alveoli (internal cement tube, particularly the strand-like extensions into the dermal tissue around thc tube). The role of the cement, in promoting firm and early anchorage during the long attachment of ixodid ticks to a host is discussed. Relaxation of the dilated mouthparts on completion of engorgement would loosen the interlock of the hypostomal teeth with the corresponding indentations in the cement tube and facilitate detachment of the replete tick.