In asthmatics, exercise (E1) is known to induce bronchoconstriction; a second period of exercise (E2) within 30 to 90 min induces a lesser degree of bronchoconstriction. The reason for the "refractory" bronchoconstrictor response to E2 is unclear. We studied 6 normal subjects (Group 1) and 12 stable asthmatics to examine the possible relationship between the refractory period and sympathoadrenal function. The asthmatics were further divided into 2 groups, based on the absence (Group 2, n = 5) or presence (Group 3) of an exercise-induced bronchoconstrictor response. In each subject/patient, after control measurements of spirometry and venous blood sampling, a standard level of treadmill exercise was performed, and blood and spirometry were obtained at 1, 5, 15, and 25 min after the end of exercise. A second period of treadmill exercise, of the same level and duration, was then performed, and blood sampling and spirometry were repeated at the same time intervals after the end of exercise. There was no significant (p less than 0.1) difference in baseline plasma epinephrine (Ep), or norepinephrine (Np) levels; however, plasma dopamine (Dp) levels were significantly (p less than 0.05) higher in Group 3. In Groups 1 and 2, FEV1 did not change significantly after the first (E1) or second (E2) exercise periods, but there were significant (p less than 0.01) changes in Group 3 (maximal percent changes in FEV1, delta FEV1%, E1 = -14.4%, E2 = -8.8%), and the delta FEV1% after E2 was significantly (p less than 0.01) less than after E1.(ABSTRACT TRUNCATED AT 250 WORDS)