To determine whether outpatient medical care obtained at federally funded rural community health centers (CHCs) in Maine acts primarily as a substitute or as a complement to inpatient care, a study of 36 communities served by CHCs was conducted. The hospital use of CHC users (age- and sex-adjusted admissions, days, and length of stay) was compared with that of nonusers from the same communities in 1980. Statistically lower rates of hospital admissions and days were observed for all CHC patients and for selected groups based on their age, sex, and insurance status (specifically Medicaid or Medicare). Hospital use of CHC community populations was then compared with that of 24 comparison communities without access to CHCs, using multiple linear regression in a pre/post design. The model tested, which included rates of health center use, insurance penetration, poverty, and hospital availability, among other factors, did not detect any differences in hospital use between CHC community and comparison populations. These results and additional data presented on selected hospital diagnoses and insurance coverage suggest that treatment, and hospitalization incentives, of CHC providers may reduce hospitalization. Clinic providers lack the economic, professional, and institutional incentives to hospitalize. Additional study to determine the actual substitutability effect is indicated.