The stag party had been to a go-kart track
The men had spent the afternoon at the Kartstart Indoor Raceway.
They were taken to hospital several hours later complaining of chest pains, nausea and headaches.
An investigation has already established that the karting centre's ventilation system and carbon monoxide gauge were working properly.
Carbon monoxide
The men were reported to have spent the afternoon at a "stag event" at the go-kart centre.
They later began to feel ill and attended the accident and emergency department at Aberdeen Royal Infirmary.
Examination revealed higher levels of carbon monoxide than would normally be expected.
Nine members of the party were released from hospital after oxygen therapy and no lasting complications are expected.
One member of staff from the raceway was taken to hospital by his parents as a precaution.
Ventilation system
The cause of the high carbon monoxide levels is being investigated and is still not clear.
Raceway managing director Craig Lockhart said the premises has a purpose-built ventilation system and carbon monoxide indicators that did not indicate abnormality.
He said no similar incidents had been reported.
He added that it was possible that the group had been involved in a longer and more strenuous period of racing than normal.
Hospital staff said anyone who feels they are suffering from the effects of carbon monoxide should seek medical advice.