The chief executive of Apple, Steven P. Jobs, who has been on a medical leave since January for treatment of what he called a hormone imbalance, underwent a liver transplant two months ago at a hospital in Tennessee, The Wall Street Journal reported on Saturday.

The newspaper said doctors had advised Mr. Jobs to return to work as planned at the end of this month, but on a part-time basis. Mr. Jobs, through his wife, Laurene Powell, declined to comment on Saturday when reached at the couple’s home in Palo Alto, Calif.

In 2004, Mr. Jobs had surgery to remove a growth called an islet cell tumor from his pancreas. That procedure, according to people briefed on his illness, created chronic digestive problems and contributed to severe weight loss.

Dr. Kara Fine, an endocrinologist in New York who has not treated Mr. Jobs, said the liver transplant might be related to the digestive problems, or to some unknown condition, and not to a spreading of his cancer.