Urinary neopterin concentrations were studied in 30 patients with squamous carcinoma or adenoid cystic carcinoma of the oral cavity. Compared to healthy controls 19 patients (63%) had increased neopterin concentrations. There was a statistically significant correlation between neopterin levels and tumor differentiation but no correlation of neopterin values with tumor size. Longitudinal studies will be necessary to evaluate a potential usefulness of neopterin concentrations to predict prognosis in squamous carcinomas of the oral cavity.