Participation of pharmacist volunteers in the medication program of a countrywide health care program for homeless persons is described. Pharmacist volunteers were brought in to manage medications for a health care program serving homeless persons in Ramsey County, Minnesota. After the pharmacy program was structured, volunteers were recruited from the community. Pharmacists duties initially focused on product management but were expanded to include establishing and monitoring the program formulary; reviewing patient records and prescriptions for allergies, potential drug interactions, and appropriate dosage; counseling patients on medication use; and consulting with other members of the health care team. The pharmacists' efforts led to improvements in monitoring and stocking of necessary medications. The cost of the pharmacy program decreased from $1800 a month to as little as $300 a month. The value of donated supplies and medications increased from $8,600 in 1991 to over $122,000 in 1994. Pharmacist volunteers helped to improve the cost-effectiveness and quality of medication use in a homeless population.