Contrast enhancement by refraction was used to visualize tumours in the rabbit lung. VX2 tumour cells were intravenously injected into a rabbit. After 14 days the rabbit was euthanized and the lungs were imaged. Refraction-enhanced X-ray images were obtained with a sample-to-detector distance of 2.65-6m. The beamline BL20B2 at the SPring-8 synchrotron radiation facility was used for the experiment, with a monochromatic X-ray beam with an energy of 33.2 keV. In the case of projection images, it was found that refraction did not help visualization of small tumours: the nodules did not show up with sharply defined edges. In tomography, tumours with a size of 1-10mm were clearly visualized, together with blood vessels with a diameter down to 0.4mm. These results show that refraction-enhanced imaging may be useful in human lung tomography to find small tumours.