Four men were travelling in a Red Toyota Starlet which hit and ditch and overturned on the Clane to Kilcock Road at Mainham at 2.30 am.
All four males were taken to Naas General Hospital for treatment, two of whom are in a serious condition.
Gardaí are appealing for witnesses who travelled the R407 this morning between 1.45 and 2.45 and who may have seen anything, to contact them.
