Resource use by asthma patients was assessed as a step in the development of a disease management program by a university teaching hospital, a health maintenance organization (HMO), and a national pharmacy benefit management company (PBM). Medication profiles and medical records were reviewed for all HMO patients who had a diagnosis of asthma and a pharmacy claim for an asthma-related drug in 1993; patients with chronic obstructive pulmonary disease were excluded. These 656 patients' use of health care resources (outpatient clinic visits, emergency room and urgent care visits, hospital admissions, and, the associated costs were determined, as were variances from the PBM's clinical guidelines for asthma. Members 0-4 years of age had the most outpatient and emergency/urgent care visits and the most hospital admissions. Forty-four of the patients received high-dose beta-agonist therapy, and 20 of these patients did not receive either an inhaled anti-inflammatory drug or a short course of corticosteroids. The 44 patients had more outpatient clinic and emergency room/urgent care visits, more admissions, and greater total health care costs than the other patients with asthma. The asthma patients' mean health care cost in 1993 was $203, compared with $110 for all enrollees in the HMO. For patients with high use of beta-agonists, the mean cost was nearly three times that for the other asthma patients. The baseline review of resource use identified aspects of medication use that were at variance with treatment guidelines for asthma patients.