To elucidate the role of angiogenesis in the carcinogenesis and progression of oral cancer, we investigated microvessel density (mVd), mast cell density (mCd) and thymidine phosphorylase (TP) expression in a series of 50 patients with T1-3 N0-1 M0 oral squamous carcinoma (OSC) and 21 patients with non-dysplastic oral leukoplakia (NDOLP). Paraffin-embedded pathological tissue was utilised for the immunohistochemical analysis of mVd and TP expression. Toluidine blue histochemical method was employed for mast cell identification. OSC and NDOLP were not significantly different with respect to mVd (mVd mean value +/- SD: 30+/-17 and 27+/-18, respectively) and mCd characteristics (mCd mean value +/- SD: 8+/-6 and 7+/-6 units, respectively). Conversely, tumour epithelia showed some degree of TP immunostaining in 100% of cases compared with 76% in NDOLP samples (p< or =0.001 by Fisher's test). A good correlation was found between mVd and mCd in both NDOLP (c.c. 0.632; p=0.002) and OSC (c.c. 0.496; p=0.000) tissue, whereas no association between TP expression and mVd or between mCd and TP status was evident. At a median follow-up of 18 months, patients with high mVd tumours showed a greater probability of survival than those with low mVd (75 and 40%, respectively; p=0.04 log-rank test). Our results suggest that the development of oral cancer epithelia is associated with a significant increase in TP expression. Conversely, the clinical outcome of OSC seems inversely related specifically to mVd.