Hastings police have charged three inmates at Hawke's Bay Regional Prison with the attempted murder of a fellow inmate.
A 33-year-old was stabbed inside a prison building three weeks ago.
He suffered chest wounds and spent several days in hospital in a critical condition.
Detective Senior Sergeant Dave de Lange says forensic tests to confirm the weapon used in the attack have not yet been completed.
He says all three of the arrested men have been charged with attempted murder and two also face a charge of wounding with intent to cause grievous bodily harm.
They will appear in Hastings District Court on Thursday.