Provincial government drug plans are the primary source of insurance for drugs taken by seniors in outpatient settings. The adequacy of this coverage has been called into question, given the increased clinical importance of pharma-ceuticals, shifts in the provision of health care from inpatient to outpatient settings, increased use of restrictive formularies, and reductions in provincial drug subsidies. To assess the adequacy of provincial coverage, we estimated what a typical single senior beneficiary of a provincial drug plan paid out-of-pocket in 1998 on prescription drugs covered by the public program, depending on his/her province of residence, level of drug consumption, and income. We compared provincial coverage for seniors with large drug costs. We also assessed provincial coverage of drugs that were introduced into the Canadian market between 1991 and 1998. The cost of drugs consumed by a senior in a given province and year was estimated by multiplying the average number of prescription drugs consumed by senior drug users by the average per-prescription costs. High drug consumption was defined as twice the average. We used the provincial drug cost sharing rules to estimate the senior's share of the total cost of drugs consumed. Mean out-of-pocket costs range from $42 to $1,302 per year, are lower for lower-income seniors, and increase with drug use, although the charge per drug decreases with the number used. There was up to a 12-fold variation among the provinces in the charges faced by seniors with similar incomes and drug use. All but one province limits costs to seniors with catastrophic drug costs, but there was 21-fold variation in the expenditure limits. The substantial variation in seniors' out-of-pocket drug costs raises questions about the distributive equity of drug subsidies in Canada. Recent evidence on the deleterious health effects of drug charges faced by seniors in Quebec and the fact that seniors in some other provinces face direct charges similar to those faced in Quebec raise the possibility of adverse consequences of drug charges in other provinces.