Talk to Howard Loadman Jr., a 72-year-old retired executive, and it is easy to understand why enrollment growth in Medicare risk health maintenance organizations has been so explosive.

As Mr. Loadman's situation illustrates, the financial savings of enrolling in an HMO and moving out of the traditional Medicare program can be enormous.

A little over a year ago, Mr. Loadman, a former vp in Europe with Airborne Freight Corp., now Airborne Express Corp., paid about $3,000 a year in premiums to Prudential Insurance Co. of America for Medigap policies for himself and his wife, Betty.

In addition, Mr. Loadman, a diabetic, paid about $2,000 a year for prescription drugs, which the Prudential policy did not cover.

Mr. Loadman, who now lives in Sarasota, Fla., said he read several newspaper stories and ads about HMOs that provided rich benefits and charged no premiums for Medicare-eligible retirees.

"It sounded almost too good to be true," Mr. Loadman said.

It wasn't an illusion. Mr. Loadman and his wife enrolled in Humana Gold Plus Plan, the Medicare Risk HMO product offered by Humana Inc.

The Humana plan provided rich medical and hospital benefits as well as a $1,200-a-year prescription drug benefit. The premium for the health care benefits package: $0.

"Literally, I am saving thousands of dollars a year," Mr. Loadman observed.

Mr. Loadman is candid in acknowledging that not all of his experiences with the HMO have been positive. For example, he was skeptical about the results of a test taken by an HMO physician, which detected blockage in the carotid arteries. The results showed a much higher blockage than earlier tests.

Mr. Loadman went outside the network to have a new test taken, which showed a much smaller blockage. He showed the new results to his HMO primary care physician, who agreed that an operation to reduce the blockage was not necessary.

But on the whole, Mr. Loadman said he is satisfied with care delivered through the HMO. He and his wife are especially pleased that many of the medical specialists they used prior to joining the HMO are in the Humana network.

And he says he has recommended the HMO to others.

"We have a number of friends we already have recommended it to. The dollar savings are just so great," he said.