An association between a low Hb-content and a poor response on radiation therapy has been established in previous years, especially in patients with squamous cell carcinomas. Whether this is linked with hypoxic conditions of the tumour or associated with tumour volume, blood loss or other conditions, is not yet known for certain. Patients with small head and neck tumours seem to form an interesting group to study this issue because several factors can be ruled out. Therefore, a retrospective analysis of 306 patients with glottic or supraglottic carcinoma was performed, to identify whether the Hb-value was of prognostic importance and whether this was linked to other patient characteristics. All patients were treated with primary radiotherapy with doses ranging from 60 to 70 Gy in 6-7 weeks. It appeared that in glottic carcinoma, the disease-free survival was significantly worse in patients with a Hb-value below normal at the start or/and at the end of therapy (p = 0.09, p = 0.0012, respectively). In patients with supraglottic carcinoma, the above mentioned difference approved only for a Hb-value below normal at the end of treatment (p = 0.05). A decrease in Hb-level of greater than or equal to 0.5 mmol/l during therapy, regardless whether the Hb-values were within or beyond normal range, reduced the disease-free survival in patients with glottic carcinoma (p = 0.0125). In a multivariate analysis, the Hb-value at the end of treatment proved to be an independent prognostic factor after T- and N-classification. There was no relationship with nutritional condition of the patient, nor with the Karnofsky Performance scale.(ABSTRACT TRUNCATED AT 250 WORDS)