Respiratory and skeletal (deltoid) muscle strength were evaluated in 34 oral steroid-dependent asthmatics by use of maximal inspiratory and expiratory pressures and a myometer. The patients were compared to age- and sex-matched asthmatics who had never been on continuous oral steroid treatment. Endurance time was also studied in ten steroid-dependent asthmatics and ten controls using a pressure threshold breathing device. Nutritional status was assessed from body weight, midarm circumference, triceps skinfold (TSF), prealbumin, albumin, and total protein. An open biopsy from deltoid muscle was taken from nine steroid-dependent asthmatics and the diameter of type 1 and type 2 fibers was measured by a morphometric study. No differences were found between study and control groups either in respiratory and skeletal muscle strength or in endurance time. Steroid-dependent asthmatics showed a decrease in TSF, total protein, albumin, and potassium serum levels when compared with the control group but differences were not statistically significant after Bonferroni's adjustment for multiple comparison studies. Transversal diameter of type 2 fibers was significantly correlated with the percentage of ideal weight (r = 0.75 p less than 0.05), but not with average daily dose of steroids nor with the length of steroid treatment. Our results support the clinical impression that steroids, at the doses usually administered in chronic severe asthma, do not cause muscular weakness. We also found that malnutrition rather than corticosteroids is the most important contributory factor to type 2 muscle fiber atrophy in steroid-dependent asthma.