Sen. Tim Johnson (D-S.D.) underwent surgery Tuesday to remove his gallbladder, his office said.

Johnson, who was hospitalized Sunday with a fever attributed to a bad reaction to medicine, underwent the procedure this morning in Sioux Falls.

Tim is in good hands and in good spirits," said Johnson's wife, Barb, in a statement. "We want to thank everyone for their prayers and support."

The senator's doctor said the laparoscopic surgery had gone "exceedingly well," and Johnson is "resting comfortably."

"All of our findings point to the gallbladder as the primary problem, but it is still possible that he is having some lingering effects from the antibiotic drug reaction," said Dr. Donald J. Wingert. "We will keep the senator in the hospital a few more days for observation."

Johnson's health scare and surgery are unrelated to his 2006 medical episode due to arteriovenous malformation (AVM), which resulted in Johnson being sidelined from his official duties for an extended period of time.