Britain would have a stronger NHS if it remains in the EU, Nicola Sturgeon said.
"You're more likely to be treated by an immigrant on the NHS than you are to be treated in the next bed to an immigrant," she said.
Ms Sturgeon added: "I wouldn't trust Boris Johnson with a health service as far as I could throw Boris Johnson."
She added that existing pressure on public services was due to budget cuts.
Campaigners for remaining in and leaving the EU have clashed in a fiery debate on ITV.
On a night of fierce debate between Remain and Leave campaigners during the ITV referendum debate, which of the claims actually stacked up?
Analysis of ITV's EU referendum debate.