Case reports are given of 25 patients with severe chronic obstructive lung disease (COLD) and with a ventilatory capacity (MVVF) < or = 35 per cent of predicted normal values. The patients were selected among persons treated 1968-1970 at the Department of Pulmonary Diseases, University Hospital, Uppsala. Clinical and physiological follow-up studies have been made. Case histories, physical and radiological findings of the heart and lungs and in 5 patients autopsy findings are given. Arterial blood gas tensions and acid-base balance in the patients' habitual state are also reported. Changes in the electrocardiograms (ECG), in lung volumes and dynamic ventilatory function and physical working capacity, measured on a bicycle ergometer, are described. In 1970-71 the patients (39-72 years of age) were admitted to hospital for 5 days in their optimal state for the following investigations: static and dynamic spirometry, total haemoglobin, ECG, vectorcardiogram (VCG), physical working capacity, pulmonary gas exchange and central haemodynamic studies. The results of the gas exchange and central haemodynamic studies, total haemoglobin and the physical working capacity are given elsewhere. Certain comparisons were made between the two groups of patients: (R) patients who had had one or several periods of manifest respiratory insufficiency with intensive treatment (n = 14) and a comparison (C) group (n = 11), with the same ventilatory impairment in regard to MVVF, but without any corresponding periods needing oxygen treatment combined with breathing assistance by a physiotherapist or respirator. Sixteen patients had chronic bronchitis with emphysema, one chronic bronchitis without emphysema, four primary emphysema, one emphysema and bronchial asthma and three emphysema and widespread bronchiectasis. The most striking difference in the clinical history of the R-and C-group patients was a greater tobacco consumption (packets/lifetime) in the R group. The ECG was typical for right ventricular hypertrophy (RVH) in one patient from each group. Slightly delayed ventricular activation and clock-wise rotation of the QRS frontal plane axis were the most common ECG findings. VCG was typical for RVH in one C-group and 4 R-group patients, and suspected to indicate RVH in 7 R- and 5 C-group patients. Biventricular hypertrophy may be one of the reasons that ECG and VCG do not more often fulfil the typical RVH criteria. The average MVVF was about 21 per cent of predicted normal values before and about 27 per cent after administration of a bronchodilating spray. The average vital capacity (VC) was 55 per cent before and 64 per cent after the use of a spray.(ABSTRACT TRUNCATED AT 400 WORDS)