We studied 14 atopic subjects with mild asthma (six men and eight females) to document whether allergen exposure can change the pattern of response to exercise. Each had an exercise test at 80% of the VO2 max for six minutes before (exercise 1) and 48 hours (exercise 2) after an allergen inhalation test (AIT). FEV1 was measured at regular intervals up to eight hours after each challenge. On the day following AIT, spontaneous changes in FEV1 were measured for eight hours (control day). Airway responsiveness (AR) to histamine was measured at the beginning of the study, then 24 hours after AIT and at the end of the 2nd exercise. Mean early fall in FEV1 after exercise 1, AIT and exercise 2 were, 24.9 +/- 3.2%, 24.5 +/- 2.2%, and 27.6 +/- 3.8%, respectively. Airway responsiveness to histamine was increased at 32 and 56 hours post-AIT with a mean PC20 (SEM) of 0.50 (0.40, 0.62) and 0.93 (0.74, 1.17) mg/mL compared with 1.87 (1.33, 2.61) at baseline (P less than .05). Allergen inhalation test induced an isolated early asthmatic response (EAR) in four subjects, an equivocal response (late fall in FEV1: 5% to 15%) in four and a definite late asthmatic response (LAR) in six. No subject had a LAR before the AIT but two with a LAR after allergen exposure developed a late response to exercise after the AIT. This last was only partly explained by an increased diurnal variation of expiratory flows.(ABSTRACT TRUNCATED AT 250 WORDS)