It is found that fat and non-fatty tissue in dissected samples of the mamma differ in their T<latex>$_1$</latex>/T<latex>$_2$</latex> ratios. This opens the possibility of locating tumours by n.m.r. imaging, because they have a lower fat content than their surroundings. By means of a sensitive point method, samples were scanned with a resolution of about 0.4 mm x 0.4 mm. The similarity between the shape of a tumour in an n.m.r. and in an X-ray image of a thin section of mamma tissue is quite convincing.