Over half of all Enterprise Ireland clients have been impacted by Brexit, according to a survey from the body.
In addition, one in ten EI firms say the UK imminent departure from the European Union has already cost them over €100,000.
Ahead of the EI International Markets week, which kicks off today in Dublin's RDS, currency fluctuations was cited by firms as the biggest concern.
This was followed by tariffs and supply chain disruption.
Julie Sinnamon, CEO of Enterprise Ireland, said: "Our research shows that Irish Exporters are already feeling the negative impacts of Brexit through their profit margins."
"We have consistently said that the wait and see approach is not an option and client companies are heeding this advice... Overall, Enterprise Ireland client companies have opened 275 new overseas presences in the first six months of 2019."
Over 650 EI client companies are expected to attend the International Markets week over the next three days.