Hypoxia-inducible factor-1alpha (HIF-1alpha) and the neo-angiogenic factors induced as a result of hypoxia-inducible factor transcriptional activation may contribute to tumorigenesis by inducing vessel formation that in turn provides oxygen and nutrients promoting tumor expansion. In vitro studies of nasopharyngeal carcinoma (NPC), an aggressive malignancy that is nearly always infected by Epstein-Barr virus, show HIF-1alpha is upregulated by viral latent membrane protein 1 (LMP1). The current study used immunohistochemistry to examine the extent to which HIF-1alpha and LMP1 are co-expressed in naturally infected NPC tissues. Analytic procedures were optimized for sensitive localization of HIF-1alpha and LMP1 in fixed tissue sections using immunohistochemistry with sensitive fluorescent and signal amplification technologies. Vessel density was quantified by CD31 immunohistochemistry. LMP1 was expressed focally in all 18 NPCs examined, including 7/8 in situ lesions. There was no consistent co-localization with HIF-1alpha which was usually only weakly expressed in a subset of neoplastic cells. Neither LMP1 nor HIF-1alpha expression correlated with vessel density, and degree of vascularization varied widely among cases. Advanced immunohistochemical technologies reveal that LMP1 is expressed more commonly than previously reported in NPC. There is no consistent relationship between LMP1 and either HIF-1alpha expression or degree of microvasculature. The biologic basis for the wide variation in vessel density deserves further investigation.