The opposition have been demanding that Health Minister Deb Matthews step down over the troubled air ambulance service, whose "financial irregularities" are under a police probe.
Those calls only got louder after the province's auditor general released a report last week saying the government gave Ornge $700 million over five years with virtually no oversight of how the money was spent.
McGuinty says he accepts the auditor's "critique" that they didn't oversee the agency, but defended his minister.
He says Matthews acted as soon as she knew something was wrong at Ornge and has taken steps to fix the problems so they don't happen again.
Conservative Peter Shurman says McGuinty is supporting an "incompetent disgrace of a minister" who should be fired for the millions that were wasted at Ornge.