Twenty-six adults (23 to 58 years) with mild to moderate asthma underwent a 10-week supervised rehabilitation program, with emphasis on physical training. In the first 2 weeks, they exercised daily in an indoor swimming pool (33 degrees C) and received education about asthma, medication, and principles of physical training. In the following 8 weeks, they exercised in the pool twice a week. Every training session lasted 45 min. The training sessions were made as suitable as possible for the individual subjects, in order to minimize "drop outs" from the program. The aim of the study was to evaluate the efficacy of the rehabilitation program and to determine if inactive asthmatic adults can exercise at high intensity. The rehabilitation program was preceded by a 6-min submaximal cycle ergometry test, a 12-min walking test, spirometry, and a methacholine provocation test. The subjects also responded to a five-item questionnaire related to anxiety about exercise, breathlessness, and asthma symptoms using a visual analogue scale. All subjects were able to perform physical training at a very high intensity, to 80 to 90% of their predicted maximal heart rate. No asthmatic attacks occurred in connection with the training sessions. Twenty-two of the 26 subjects completed the rehabilitation program, felt confident with physical training, and planned to continue regular physical training after the 10-week program. Improvements in cardiovascular conditioning, measured as a decreased heart rate at the same load on the cycle ergometer (average of 12 beats/min), and as a longer distance at the 12-min walking test (average of 111 m), were observed during the program. FEV1 increased significantly from 2.2 to 2.5 L. Forced expiratory flow at 25% of vital capacity also increased slightly but significantly. Methacholine provocation dose causing a fall in FEV1 by 20% was unchanged. Seventeen subjects had a peak expiratory flow reduction of more than 15% after the preprogram ergometry test and were classified as having exercise-induced asthma (EIA). Only three of these subjects had EIA after 10 weeks. The asthmatic subjects were less afraid of experiencing breathlessness during exercise and less anxious about exercising at a high intensity after 10 weeks (p < 0.05). The asthma symptoms abated significantly during the rehabilitation program and the subjects needed less acute asthma care after the rehabilitation program. The results indicate that asthmatic persons benefit from a rehabilitation period, including physical training. Rehabilitation programs are therefore of value as a supplement to conventional pharmacologic treatment of asthma. This rehabilitation program can be adapted for use in clinical practice.