Tumour oxygenation status was measured by a polarographic needle electrode in 31 patients with lymph node metastasis of squamous cell carcinoma of the head and neck and 18 patients with primary soft tissue sarcoma. Two oxygenation parameters, the median pO2 and the proportion of measured values less than 5 mm Hg, were used in comparing the inter- and intrasubject heterogeneity in tumour and subcutaneous tissue. Results of the analysis may be summarized as follows: 1) the variation in oxygenation between tumours was significantly greater than that within tumours, 2) the variation in oxygenation of subcutaneous tissue between patients was significantly greater than the variation within patients, 3) oxygenation of tumour was significantly lower than that of subcutaneous tissue, 4) no significant difference in the distribution of the oxygenation parameters in the two tumour types, and 5) both oxygenation parameters correlated. In conclusion, measurements by oxygen electrodes were able to distinguish intratumour heterogeneity from intertumour heterogeneity provided that several electrode tracks were done. The method therefore appears to be feasible for differentiation of tumour oxygenation clinically.