The impact of HMO enrollment on utilization and satisfaction in a sample of industrial employees was investigated using a panel study design. Preenrollment and postenrollment ambulatory utilization rates, out-of-pocket costs, and measures of satisfaction are presented for enrollees in two closed- and one open-panel HMO-type plans. Their health care experiences are compared to those of reenrollees remaining in the HMOs during both surveys, as well as to those retaining their Blue Cross-Blue Shield membership. Lack of access to and dissatisfaction with previous sources of care distinguished the preenrollment experience of those who selected the closed-panel plans; their postenrollment experience produced increasing satisfaction reflecting that their expectations in these areas were met. Continuing enrollees in closed-panel plans were somewhat less satisfied after a year of experience than they were earlier. Those who joined the open-panel plan did so because of the expanded benefits and financial advantages which, their postenrollment experience showed, were accurately perceived. Utilization patterns also changed: continuing enrollees in both types of plans made fewer illness but more preventive visits; new enrollees used greater numbers of both types of services after enrolling than before.