The former jockey, 69, went under the knife at Oxford's Churchill Hospital in England last weekend (29-30Jan12) and is now recuperating at home.
Pitman, whose kidney was successfully transplanted to a mystery recipient, felt compelled to become a donor after seeing his friend Tim bounce back from kidney failure after receiving a new organ.
He says, "I was watching him dying in front of my eyes and I have since seen him blossom. He went from dropping off to absolutely zinging.
"Not knowing who will receive the kidney doesn't bother me. I just want to help anyone who was suffering like Tim was. The point is you have two (kidneys) and you only need one.
"I feel great. I feel it was worthwhile and I feel strong. I am pleased I did it for that reason and I am pleased it worked."