Hundreds of households have been warned to take action against high levels of a gas thought to lead to lung cancer.
Radon is a natural radioactive gas that comes from minute amounts of uranium found in rock and soil and although levels are generally low, it is believed to lead to more than 1,000 deaths across Britain.
Testing kits were sent to some people across Aberdeenshire and the Highlands last year. Higher-than-normal levels of the gas were detected in more than 800 properties.
Concentrated pockets were found particularly along Deeside in the north east, according to an indicative map published last July.
Neil McColl, of the Health Protection Agency's centre for radiation, chemical and environmental hazards, said: "We fully understand that when some people received their radon results they may have been surprised or even a little concerned because having a letter drop through the door telling you that your family is exposed to radiation could be unsettling for some people.
"Sadly, ignoring radon isn't a safe option. Failing to deal with high radon levels just increases your exposure and the risk to the health of you and your family. We are here to help and want to say to those who, for whatever reason, missed us when we ran local events that we're only a phone call or an email away."
Radon produces a radioactive dust in the air, the agency said. The dust is trapped in airways and emits radiation that damages the inside of lungs.
Public Health Minister Michael Matheson said: "We are encouraging everyone who has received high radon results to come forward and find out more about radon and what they can do to their homes to lower levels.
"Radon cannot be detected by sight or smell but we now know that hundreds of homes across the north of Scotland have higher-than-safe levels. Failing to deal with high radon levels increases your exposure to it and in the long term this can be a health risk."
Householders wanting more information can call 01235 822 622 or email email@example.com.