Generous contact efforts were used to recruit 3,004 respondents into the first wave of the St. Louis Epidemiologic Catchment Area (ECA) project, a psychiatric epidemiologic study of the general population, conducted from 1981-1982. These efforts were analyzed to establish which sociodemographic characteristics or current psychiatric disorders were determinants of difficulty in recruitment. Being young, male, black, a nonrural resident, educated, and full-time employed were the demographic characteristics associated with increased contact efforts. Persons currently meeting criteria for an alcohol disorder required almost 20% more contact attempts than those without the disorder; this difficulty lay both in their being less available for an initial contact and refusing at a higher rate once contacted. An optimal recruitment effort cutoff point is provided, and a method is suggested for detecting that optimal point in the course of ongoing studies.