A ward at Raigmore Hospital has been closed to new admissions and transfers due to an outbreak of Clostridium difficile (C. diff).
Two cases of the bug have been confirmed in 7C, a medical ward at the hospital in Inverness.
NHS Highland said patients on strong antibiotics were the worst affected by the bacterium.
Dr Jonty Mills, a consultant microbiologist at Raigmore, said the situation was under control.
He added: "The routine monitoring we have in place means we have been able to react quickly and take decisive action to contain the outbreak at an early stage."