The emergency services were called to Clynelish Distillery in Brora after the accidental mixing of two substances resulted in the production of chlorine gas.
The alarm was raised at 6.54pm on Tuesday and around 30 firefighters went to the scene.
A spokesman for the distillery said the contract worker was taken to Raigmore Hospital in Inverness as a precaution and was discharged this morning.
Two fire appliances from Inverness, one from Golspie, one from Helmsdale, one from Invergordon and the control unit and environmental pod from Inverness were all dispatched to the scene.
A spokesman for the Fire and Rescue Service said: “An issue during the decanting process resulted in the accidental mixing of two substances which resulted in the production of chlorine gas.
“One man, who was in the area at the time and was exposed to the gas, was taken to hospital for treatment suffering from breathing difficulties. He was kept at Raigmore Hospital in Inverness overnight for observation.
“Firefighters in gas tight suits and breathing apparatus, with technical support provided by the SFRS’s National Hazmat Technical Support Team, isolated the tank and made the area safe prior to the arrival of a specialist clean up company.
“Crews then entered a portable decontamination unit as a precautionary measure. None of the firefighters were exposed to the gas.”
Group Manager John MacDonald said: “This was an incident with potentially serious outcomes, but due to the quick thinking of on-site staff at the distillery and the response from the emergency services, the incident was dealt with quickly and effectively.
“We are pleased that no one has been seriously injured and that we managed to help bring the incident to a successful conclusion.”
A spokesman for drinks giant Diageo, who operate Clynelish, said: “There was an incident involving a contractor working at the cooling tower at the distillery.
“The health and safety of our staff and our contractors is paramount and we took the necessary action under the circumstances to ensure the wellbeing of the contractor. He was taken to hospital as a precaution and has now been discharged is returning to work today.
“The emergency services attended the site as a precaution. There has been no damage of any sort as a result of the incident and the distillery is operating as normal.”
Clynelish Distillery produces Sutherland’s only single malt whisky.