Previous studies indicated that the prevalence of symptomatic asthma is about 4 to 7 percent. No similar studies exist to suggest the prevalence of asthma in highly trained competitive athletes, since asthma is thought to be an uncommon disease in this population. We became concerned, therefore, when a large number of football players developed symptoms consistent with asthma during preparation in California for the Rose Bowl in December 1981. We studied the team and found 12 percent of the football players admitted to a history of asthma, whereas none of the members of the university basketball team and 7 percent of a group of sophomore medical students and physician assistant students gave a history of asthma. Furthermore, 19 percent of the football players indicated that at some time they had chest tightness, cough, wheezing, or prolonged shortness of breath after exercise; 12 percent of the basketball players and 37 percent of the students indicated such a history. We examined each of these three groups for non-specific bronchial hyperresponsiveness to inhaled methacholine using a modified methacholine bronchoprovocation (MBP) challenge and found that 76 of 151 (50 percent) football players tested had positive tests; 76 percent of those with symptoms had positive results of inhalation tests and 47 percent of those with minimal or no symptoms had positive test results. In addition, four of 16 (25 percent) basketball players and 69 of 167 (41 percent) students had positive MBP tests. These studies indicate that bronchial hyperresponsiveness to inhaled methacholine is much more common in these young adults than has previously been suspected.