The clinical and radiological features of 23 patients with cor pulmonale due to chronic obstructive airways disease were reviewed. Twenty-two patients had evidence of pulmonary vascular disease and 52 per cent had secondary polycythaemia. Eighteen (78 per cent) had radiological evidence of emphysema. Thirteen of the patients (56.5 per cent) had alpha 1-antitrypsin phenotypes associated with serum deficiency and of these the largest single group was the MZ phenotype (34.8 per cent). No difference was found between the clinical features of patients with the MM phenotype or those associated with alpha 1-antitrypsin deficiency, although radiological emphysema was more common in the latter group (92 per cent compared to 60 per cent).