Desmond Swayne (New Forest W) urged the Leader of the House, Margaret Beckett, to help determine Mr Blair's sanity. He was referring to an article in The Independent by Paul Flynn (Lab Newport W) on Labour's handling of the London mayor selection process.
Mr Flynn accused Mr Blair of ignoring the lessons of devolution in Wales. "Continuing to do the same thing and expecting to get a different result is the definition of madness given by Alcoholics Anonymous to drunks who boast that they have learnt to manage their boozing."
Mr Swayne said: "Only Madam Speaker, under the procedures laid down in Section 141 of the 1983 Mental Health Act, can determine whether an MP is sane or insane.
"You might consider that you would assist her if you were to enable the Prime Minister to come to the House and make a statement next week because, with the greatest respect, at Prime Minister's question time it is very difficult to judge, with so many other excitable interventions from Labour members."
To laughter, Mrs Beckett replied: "I am familiar with the varied and colourful phraseology frequently adopted by Mr Flynn."
Mr Blair would be in the Commons next week to make a statement on the Helsinki summit, she said, adding: "I think both his sanity and his effectiveness are not doubted anywhere except perhaps on the Tory side."
The exchange followed Mr Flynn's attack first made in Campaign Group News, a left-wing newspaper. He warned: "The deafening message from Wales and Scotland is 'don't stitch the choice of candidate in London'. "
He said the likely explanation for Mr Blair's approach was "the neurotic need of the leadership of the party to control every activity in minute detail".