NMR imaging was performed on 12 patients with cerebral tumour before and after administration of intravenous gadolinium diethylene triamine penta-acetic acid (DTPA) (0.1 mmol/kg). Contrast enhancement was seen in all cases. Ring enhancement was most frequent (7 cases) but central, linear, patchy, and diffuse enhancement were also seen with both inversion-recovery and spin-echo sequences. The degree of enhancement was greater than that seen with X-ray computed tomography (CT) in 8 cases, equal to it in 3 cases, and less in 1 case. NMR distinguished between tumour and peritumoral oedema to the same extent as did CT. No side-effects were encountered and there was no significant change in urea, creatinine and electrolytes, liver function tests, blood coagulation, or urine testing after administration of gadolinium-DTPA. Gadolinium-DTPA is likely to be of considerable value in NMR imaging of the brain.