Four people were tonight being tested for the deadly swine flu, it was confirmed.
Health chiefs said a fifth sample tested for the virus which has been responsible for dozens of deaths in Mexico was negative.
The first British cases of the killer flu were confirmed tonight in Scotland.
Professor Bill Hall, chair of Ireland’s National Pandemic Influenza Expert Group, said the four suspected cases are not very ill and have not been admitted to hospital.
“Suspected cases is a clinical diagnoses,” said Prof Hall.
“We receive the samples. We leave it up to the judgment of the physician or whoever is evaluating the patient to decide it was a test for this virus.
“We had one test yesterday which was negative and we are carrying out four tests today.”
The Health Service executive (HSE) warned many more samples will be received from GPS in the coming weeks as holidaymakers return from long-haul trips with flu like symptoms.
A HSE spokeswoman said results for the four people will be known in the morning.
More than 100 people have so far died of an outbreak in Mexico which has prompted fears of a global epidemic similar to worries over avian flu in 2005.
Health officials said Ireland is prepared for a possible outbreak and has stockpiled enough drugs and masks to tackle any infection of swine flu.
Chief Medical Officer Dr Tony Holohan said plans are in place to tackle any eventuality, up to and including the possibility of very large infection rate in the population.
“We can’t predict exactly what we are going to see, but we are planning on the basis that we will see cases and we are planning to ensure we are ready to deal with that eventuality,” he added.
Experts from the HSE, the Health Protection Surveillance Centre and the Department of Health and Children are monitoring the situation very closely.
The HSE’s head of health protection, Dr Kevin Kelleher, said advice has been issued to GPs and clinicians nationwide on managing any suspected cases.
“It is important to be prepared for any possible cases that may arise,” said Dr Kelleher.
“Ireland has been preparing for situations like this for several years, and we have robust and detailed plans in place to respond.
“The H1N1 swine flu virus is sensitive to the anti-viral drugs of which we have in place ample stockpiles for Ireland. We are and will continue to closely follow the emerging situation.”
In Mexico, more than 1,400 possible cases of pneumonia linked to swine flu have been identified since mid-March and 103 people have died.
In the US, 20 cases have been confirmed in California, Texas, New York and Ohio, with more cases discovered in Europe during the day.
Symptoms of the flu include fever and respiratory tract illness (cough, sore throat, runny nose), headache, muscle aches and possibly vomiting and diarrhoea.
Health Minister Mary Harney is due to attend a meeting of EU health ministers in Luxembourg on Thursday.
The situation is under ongoing review by the World Health Organisation (WHO) and the Department of Foreign Affairs also urged Irish citizens travelling in Mexico to ’exercise extreme caution’ in coming days.
Mr Martin told his EU colleagues at the General Affairs & External Relations Council meeting in Luxembourg that close co-ordination between member states on the issue was vital in coming days.
“The EU is on red alert and Ireland’s national response systems have been fully mobilised,” he added.