The purpose of this longitudinal study was to describe mortality and change in lung function in adults with bronchial asthma, and furthermore to investigate a potential difference in the prognosis for patients with intrinsic and extrinsic asthma. Out of 213 asthmatics admitted to our hospital, 170 (82%) participated in a 10-year follow-up examination; according to the tests for extrinsic asthma at the first examination, the patients were divided into 117 patients with intrinsic asthma and 53 subjects with extrinsic asthma. Twenty-seven (13%) patients, 23 with intrinsic and 4 with extrinsic asthma, died during the observation period, which was almost twice the number expected in both intrinsic and extrinsic asthmatics, but because of the small number of patients with extrinsic asthma, the findings were statistically significant for the intrinsic asthmatics only (p less than 0.05). Seventeen (8.2%) died of pulmonary diseases, of whom 9 (6 patients with intrinsic asthma) died in an acute attack of bronchial asthma. After a questionnaire concerning respiratory symptoms had been answered, a lung function test was performed in all subjects in both 1976-1979 and 1988. A histamine challenge test was performed at the examination in 1988. Of the 143 subjects who were re-examined in 1988, 96% still had respiratory symptoms. The first lung function test in 1976-1979 showed no difference in FEV1 (% predicted) between the two groups, whereas the annual mean loss of FEV1 during the observation period for the intrinsic and extrinsic asthmatics was 50 ml and 22.5 ml, respectively (p less than 0.0001). Decline in FEV1 was found to be independent of smoking habits in both patient groups. We found that the decline in lung function increased with increasing age in both intrinsic and extrinsic asthmatics (p less than 0.001 and p less than 0.05, respectively). The so-called "horse-racing effect" could be demonstrated for the patients with extrinsic asthma (p less than 0.003); whereas no significant relation was found between FEV1 at the time of enrollment and decline of FEV1 for the intrinsic asthmatics. We conclude that asthmatic subjects have an excess mortality and that the prognosis for intrinsic asthma is worse than that of extrinsic asthma with regard to rate of decline in lung function.