We report our experience with the technique of lymphatic mapping using patent blue V dye in patients with limb malignant melanoma. The technique is based on the hypothesis that embolic metastases occur along lymphatic channels to a 'sentinel' lymph node: the draining lymph node nearest the site of the primary malignant melanoma. Patent blue V dye (0.5-1.0 ml) is injected intradermally around the site of the melanoma. Immediately the groin or axilla is opened and the blue lymphatic channels followed to the sentinel node. The node is removed and examined by both haematoxylin and eosin (H&E) and immunohistochemical staining. We have carried out this technique in 35 patients, all of whom had 'clinically assessed' stage I disease. In all 35 patients, sentinel nodes were identified, and nine were found to contain unsuspected micrometastases. Our initial evaluation of intraoperative lymphatic mapping is very promising. The technique is practicable and easy to master. If 25% of patients with cutaneous malignant melanoma who are clinically stage I have nodal disease, this has great importance not only for staging and treatment but also for all future therapeutic trials.