Carwyn Jones has apologised to Plaid Cymru AM Adam Price after criticising him using inaccurate information.
The first minister said last week Mr Price had ignored requests to take part in a consultation on a shake-up of services at Hywel Dda health board.
Hywel Dda said later Mr Price had asked to see its chief executive and it was sorry false information was released.
On Tuesday, Mr Jones made a statement in First Minister's Questions in which he apologised to the Plaid AM.
Mr Jones said: "Following the exchange in First Minister's Questions last week, I want to apologise to the member for Carmarthen East & Dinefwr for the answer I gave to him.
"He will know that we have both received apologies too from the health board in relation to the incorrect information on which our exchange was based.
"I do believe that information was passed to my office in good conscience, and was subsequently passed on to me equally in good faith."
Mr Jones said he wanted to make clear "this is not information I had personally requested in any way shape or form".
But he said "it was information that I chose to use - and on reflection I do not think last week was worthy of the exchanges we should promote in this, our Welsh parliament.
"I apologise for my part in that."
A spokesman for Mr Price said it was "right for the first minister to go to the assembly chamber today to apologise to Adam Price, and to acknowledge that his contribution last week was not befitting of the Welsh Parliament".
"We continue to have profound concerns regarding the relationship between the Welsh Government and independent public bodies, and the way in which confidential information about elected members is sought and used."
The spokesman said Plaid Cymru would "continue to pursue these concerns rigorously", adding "today's apology does not remove the need for the first minister to refer himself to the independent advisor on the ministerial code".
The ministerial code is a list of rules by which ministers are expected to operate.