People allergic to the privet plant are being invited to take part in an allergy trial.
The Waikato Regional Council is already getting its usual seasonal rise in complaints about privet as it starts to flower.
A council biosecurity officer, Darion Embling, says there's no definitive proof that the plant causes allergic reactions, but the council is keen to know more about how people are affected by it.
Next month's trial through the Auckland Allergy Clinic will involve a prick-test and a questionnaire.
Under council rules, land-owners are required to control privet on their property if a valid health-related complaint is received from neighbours.
People wanting to take part should call the Waikato Regional Council 0800-800-401