The Health Service Executive has proceeded with plans to reconnect its internal IT network to the outside.
In a series of tweets, Director General Tony O'Brien said a careful and considered decision had been made to reconnet to external email.
However he added that the threat was not yet over and vigilance was required.
The system was disconnected as a precaution on Friday afternoon in response to the emerging threat from the WannaCry ransomware virus that was sweeping the world.
The organistion took the decision to cut external communications as the NHS in England came under attack.
It meant nobody inside the HSE could receive emails from outside or access the internet or external based platforms.
The decision coupled with preventative measures seems to have kept the ransomware away from vulnerable machines on the network.
Yesterday the HSE's internal email system was reactivated.
The organisation's IT team has also updated tens of thousands of PCs and servers with the latest anti-virus and security updates.