A technique of in situ deep venous valve construction based on vein wall intussusception is described. The technique has been used to construct a size-matched, autogenous valve in the femoral vein of the dog. Forty-one valves have been constructed. Immediately after construction, all 41 were patent at ascending phlebography and Harvey's test showed them to be competent. Descending phlebography demonstrated competence in 38 valves. Hydrostatic testing was performed on 27 valves in the vertical position at pressure gradients in the range 0.2-250 cmH2O. Of these, 24 valves were fully competent. Six valves were studied at intervals between 1 and 112 days after construction. All six were competent by Harvey's test and five were competent at descending phlebography. There was no evidence of thrombosis in any valve. This technique may be suitable for replacement of deep venous valves in patients with the calf pump failure syndrome caused by deep venous reflux.