Blastemal cells arise after the amputation of limbs or tails in urodele amphibians. These histologically undifferentiated mesenchymal cells divide and subsequently differentiate to regenerate a new appendage. Various studies (reviewed in ref. 1) indicate that blastemal cells arise from tissues near the site of amputation, including muscle, cartilage, nerve and dermis. The multinucleated myofibre, however, is a controversial source of blastemal cells. The suggestion that myofibres can dedifferentiate is based on their histological appearance during the early stages of limb regeneration. This is contrary to the widely accepted view of muscle regeneration in higher vertebrates which attributes it to satellite cells. One prediction of the dedifferentiation hypothesis is that a population with properties of both myofibres and blastema cells should be present during the early stages of regeneration. Here we described the isolation of two monoclonal antibodies, one that recognizes an antigen found only in myofibres and another that recognizes an antigen restricted to blastemal cells. By using these antibodies as cell markers, we can detect a small population of cells in the regenerating limbs of adult newts that bear both the myofibre and blastemal cell antigens. The time and location of these double-labelled cells supports the idea that blastemal cells originate, in part, by dedifferentiation of myofibres.