Micheál Martin has launched a blistering attack on Health Minister, Simon Harris, accusing him of being "poor" and "ineffective" in his job.
It comes as Mr Harris said is galling to take a lecture from the Fianna Fáil leader on health spending, citing his record in the position.
But speaking at his party's think-in in Gorey, Co Wexford, Mr Martin said it is "incredible" that Mr Harris would accuse him of failing to keep control of costs when he was Minister for Health between 2000 and 2004.
"It's just so untrue in the sense that if you actually go back to about 2010, 2011, 2012, actually the HSE budgets were within target.
"It's about 2012 onwards, that seriously gets out of target and what's happening from 2015 onward and you can look at this objectively and look at the figures at 2015 onwards is getting political."
Mr Martin accused the Government of "deliberately underestimating" the health spend which has lead to "massive supplementaries".
The Fianna Fáil leader said his party transformed care of heart disease and cancer care in this country and introduced the smoking ban.
"I can't point to similar interventions from Simon Harris or indeed from Leo Varadkar when he was Minister for Health," he said.
Taking direct aim at Mr Harris, he added: " I don't think he's an effective Minister and I think he has been a very poor minister on a number of fronts.
"I think one of the worst decisions was to offer a free test to every woman at the height of the cervical screening controversy that has caused consistent damage to that programme - has put it under enormous strain. And he didn't tell the full story about it."