This study describes the utilization of anti-asthma medications in two groups of users of such medications in the province of Quebec, Canada, during the year from June 1, 1990, to May 31, 1991. It is based on a secondary analysis of existing data banks recording the medications reimbursed by two government-funded ambulatory drug reimbursement programs that cover individuals aged 65 and over (seniors) and income security (welfare) recipients (ISRs). The study analyzed the use of the anti-asthma medications included in the list of medications eligible for reimbursement for program beneficiaries. Use was studied in two random samples of individuals who had at least one prescription filled for an anti-asthma medication (2566 seniors and 3695 ISRs). The most commonly used medication in both groups was inhaled salbutamol 100 mcg. Various forms of theophylline tablets were also used by a high proportion of the sample studied. Over 75% of the seniors and 68% of the ISR group used at least one form of theophylline during the course of the year. Inhaled corticosteroids were used by 43% of the seniors and by 36% of the ISR group, and sympathomimetics (beta 2-agonists), by 63% of seniors and 68% of ISRs.