Hæmosiderin may be deposited in the lungs in any disorder causing pulmonary hæmorrhage but, so far as is known, in only two diseases can the deposits be shown radiologically. Pulmonary hæmosiderosis in children seems to be a rare disease characterised by anæmia and occasional hæmoptysis. The X-ray picture is one of miliary shadows in the lungs which can be shown at post-mortem examination to be due to focal accumulations of iron pigment. I have not seen an example of this condition myself, although I know of two recent cases in the neighbourhood. Hæmosiderosis of the lungs, sufficiently dense to affect the X-ray picture, has also been recognised as occurring very infrequently in cases of mitral stenosis, and it is this disorder in which we are particularly interested. In 1943 a male, aged thirty-eight years, was admitted to Professor McNee's wards with cardiac failure. He gave a history of rheumatic fever eleven years previously, with subsequent dyspnœa on exertion. Ever since then he had suffered from breathlessness and, latterly, had been confined to bed with cardiac failure. The clinical findings were those of mitral stenosis and auricular fibrillation. X-ray examination of the chest showed miliary opacities in both lungs—an appearance which suggested miliary congestion. However, during an illness which lasted seven months, the small opacities remained comparatively unaltered and this, to my mind, argued against congestion as a cause and in favour of some other lesion.