Peripheral blood lymphocyte subsets were studied in 29 untreated Chinese nasopharyngeal carcinoma (NPC) patients and 20 normal controls of similar age range and sex ratio with indirect immunofluorescence using monoclonal antibodies. The percentage T lymphocyte (T11) count, percentage and absolute T helper (T4) lymphocyte counts and the T helper/T suppressor-cytotoxic cell ratio (T4/T8) were significantly lower, while the percentage and absolute T8 counts were significantly higher in NPC patients. Concerning B lymphocytes, B1 cell count was normal while B4 cell count (B lymphocytes including early B lymphocytes) was significantly lower in NPC patients. These various lymphocyte subset changes were not related to the clinical stage or to Epstein-Barr viral IgA viral capsid antibodies and IgA early antibodies. The pathogenetic and prognostic significance of peripheral blood lymphocyte changes in NPC requires further investigation.