Alveolar haemorrhage is usually, but often belatedly, diagnosed in patients presenting with haemoptysis and radiological alveolar syndrome. Its occurrence frequently marks a turn for the worst in the course of a systemic disease, since its prognosis is sombre. Recognizing its early signs might enable treatment to be instituted and prognosis to be improved. In the presence of typical alveolar haemorrhage, if high-dose corticosteroid therapy and immunosuppressants do not improve the symptoms within 48 hours plasmapheresis must be started. Alveolar haemorrhage must be considered a vital emergency justifying this therapeutic approach without waiting for the hypothetical diagnosis of the underlying systemic disease.