The Irish Cancer Society (ICS) is hoping to raise €3 million today during its annual Daffodil Day campaign.
However, ICS chief executive John McCormack has said there are concerns that poor weather conditions could affect the fundraising efforts.
"We are concerned about the weather this morning, we have thousands of volunteers all over the country who have taken a day off work, who have changed their schedules in order to go out and sell daffodils for the Irish Cancer Society," Mr McCormack said.
The groups is targeting the funds at the provision of free nationwide nursing services to people with cancer and their families all over Ireland. Last year the campaign raised €2.9 million.
Daffodil Day money also funds the National Cancer Helpline (Freefone 1800-200700), which is staffed by specialist nurses who offer free confidential information and advice to anyone worried about any aspect of cancer prevention, early detection, diagnosis and treatment.
The helpline takes some 7,000 calls per year.
"The numbers of new cases of cancer are increasing by about 1.5 per cent annually, mainly due to the growth in our population and increased life expectancy," Mr McCormack said.
"In light of this steady increase, there is an ever-growing need for our nursing care services. Since it's inception, 18 years ago, Daffodil Day has raised approximately €28 million to support and grow these services.
"We ask the Irish public yet again to give generously and ensure that we reach this year's target of €3 million".