Employees joining or not joining three newly marketed prepayment plans were surveyed during the first marketing period and during another open enrollment period 18 months later. In the 1973 survey the respondents were 149 subscribers (family contracts covering 568 persons) to the new plans and 224 nonjoiners (a total of 802 persons in their families)--all employees of Rochester's largest industry. In the 1975 survey the respondents were employees of several companies. They included 326 joiner families (1,101 persons) and 145 nonjoiner families (483 persons). There were no significant differences in previous out-of-pocket health expenditures between joiners and nonjoiners. Their self-reported health ratings did not differ; disability over the last 2 weeks was about the same. Physician utilization rates and inpatient rates were similar, except for the spouses of subscribers to one plan. However, the joiners were younger, had lived in Rochester for a shorter period, and had made less use of physicians in private practice. The three prepayment plans appealed to different population groups. The Network joiners were young, low-income families, mostly from the city. The Group Health joiners were young families with few children who especially valued availability, accessibility, and comprehensiveness. Health Watch joiners were older couples who preferred to use the traditional avenues to health care.