47 newly diagnosed patients with nasopharyngeal carcinoma (NPC) were studied using the proliferating cell nuclear antigen (PCNA) immunostaining technique. The results were reproducible as shown by assessment of three separate sections performed for each patient. No statistical correlation was found between PCNA labelling index (LI) and Ho's clinical staging or time required to achieve complete remission of the local disease. A higher PCNA LI was associated with a poorer disease-free survival. The literature on the use of PCNA in human tumours is reviewed.