Charge data from two Medicare HMO demonstration projects were analyzed to determine if prepaid plans achieved cost savings for enrolled beneficiaries. Fallon Community Health Plan of Massachusetts did not reduce total charges significantly for survivors in their first year postenrollment. However, the plan enjoyed reductions in total charges per month after the first year of nearly 38 percent (41 percent for Part A; 31 percent for Part B). Savings for decedents were more modest, reducing total charges per month by around 27 percent (19 percent, Part A; 68 percent, Part B). Greater Marshfield Community Health Plan of Wisconsin was not successful in controlling charges during the demonstration period. Marshfield incurred losses in the first postenrollment year for survivors due to a 38 percent increase in total charges per month (18 percent, Part A; 73 percent, Part B). In the second year postenrollment, the Marshfield plan was able to reduce losses for survivors to roughly 11 percent (-6 percent, Part A; 44 percent, Part B). For decedents, Marshfield experienced an increase in total charges per month of approximately 21 percent relative to fee-for-service comparisons, with Part B charges again much higher than those of the comparison group (47 percent).