The histological distribution of lipiodol within hepatocellular carcinoma (HCC) was correlated with that seen on computed tomography (CT), arteriography and high resolution plain films of 15 resected specimens. By means of special stains, the arterially administered lipiodol was shown to be maximally distributed at the periphery of large tumours and nodules. The centre of large lesions often remained unopacified. In multinodular tumours some nodules were heavily stained while others contained little or no contrast medium. In small tumours there was a more uniform distribution. In large tumours, those areas where there are large arteries (and slow flow) contained little or no lipiodol. There was also no consistent match of areas of angiographic blush with lipiodol deposition. The lipiodol patterns were poorly shown by CT when compared with high resolution films taken on a mammography unit. We conclude from this study that lipiodol on its own as an embolic agent or as a chemotherapeutic carrier has great limitations because of its peripheral and otherwise haphazard distribution in large tumours. However, such treatments might be more effective in small tumours where a greater concentration of lipiodol is likely. Nevertheless, lipiodol staining of tumours remains a useful diagnostic aid as small HCC can be difficult to visualize both on arteriography and conventional CT.