31P MR spectroscopy of human brain tumours is one feature of magnetic resonance imaging. Eight patients with large superficial brain tumours and eight healthy volunteers were examined with 31P spectroscopy using an 8 cm surface coil for volume selection. Seven frequencies were resolved in our spectra. The spectra from patients with brain tumours showed a great scatter, but generally they overlapped those obtained in normal brain tissue. No characteristic pattern of the spectra was seen in the tumours. One patient with a metastasis from a small cell carcinoma of the lung was examined before and after chemotherapy. The spectra showed considerable changes during chemotherapy. It is concluded that 31P spectroscopy using surface coils is of limited value for tumour characterization, but may add useful information in monitoring the effect of chemotherapy.