There is some evidence that endogenous progesterone and oestrogen levels influence asthma severity in females, but little is known about the effects of hormonal contraceptives. This study aimed to describe how females with asthma perceived the effects of hormonal contraceptives on symptom severity, and to describe the association between asthma severity and current use of hormonal contraceptives.A questionnaire was sent to 891 females with asthma aged 20±30 yrs recruited from general practice registers in South London, UK. It asked about perceptions of the effects of hormonal contraceptives on asthma severity, about current use of hormonal contraceptives, and included an asthma quality of life questionnaire as a measure of asthma severity.About 6% of respondents who had ever used hormonal contraceptives reported that these had influenced asthma severity,~4% reporting worsening and 2% an improvement. There were no significant differences in asthma quality of life score between females currently taking hormonal contraceptives and those not, between those taking combined and progesterone-only preparations, or between users of different progestagen types.This study found no evidence of any important effect of hormonal contraceptives or their components on asthma severity in a group of females with relatively mild asthma. Eur Respir J 1999; 14: 1028±1033. Endogenous oestrogen and progesterone level may have an effect on asthma severity in females. About a third of females with asthma report worse symptoms in the perimenstrual part of their cycle [1±4]. In a study in the USA, a higher proportion of asthmatic females was admitted to hospital in the perimenstrual part of the cycle than at other times [5]. Studies of objective measures of asthma severity over the menstrual cycle are less consistent. Three studies found no difference in bronchial hyperresponsiveness (BHR) at two different times of the menstrual cycle [6±8], though the subjects may not have been representative of all asthmatic females, the sample sizes were small, and the times of the menstrual cycle chosen for measurement of BHR may not have been those most likely to show differences. In one study of 9 females, however, BHR increased in the luteal phase [9]. Because of the inconsistency between these studies, firm conclusions cannot be drawn about the effect of endogenous hormones on asthma severity in females.There is little published research on the effect of exogenous sex hormones on asthma and the results are also inconsistent. In the study by TAN et al. [9] the luteal phase increase in BHR was much smaller in 9 females taking oral contraceptive pills, suggesting a beneficial effect on asthma severity, though no differences in symptom outcomes were demonstrated. Some case reports and uncontrolled studies suggest that oestrogen or progesterone improve asthma symptoms or lung function [10±12] but others suggest that they might cause a deterioration [13± 15]. Females who had ever used hormone replacement therapy had a higher incidence of asthm...