A study of the demand for medical care. The roles of the factors most affecting this demand in general, and the demand for urban neighborhood ambulatory medical care in particular, are hypothesized and then analyzed statistically in terms of the Queensbridge Health Maintenance Service, a clinic set up in November 1961 for residents of a housing project for the elderly. The sample consists of 1219 of the approximately 1400 residents. Health status, income, education, and price variables (especially travel distance) are the most powerful determinants of patterns of medical care. Education and income are positively correlated. When income and other variables are held constant, education encourages use of clinic services, and color is not important. On the whole, there are substantial social and economic barriers to the receipt of ambulatory care even when it is provided without charge at a convenient location. 42 pp.