Samples are sent for analysis and used in any prosecution
Bus drivers on Teesside are to be issued with DNA testing kits to help catch spitting yobs.
The sterile swabs, used to keep saliva for testing by police against national DNA databases, are being handed out to drivers employed by Stagecoach.
The move, by Cleveland Police, follows a successful trial in the neighbouring Northumbria force area.
A spokesman for Stagecoach said the measure sent a "clear message" that abusive behaviour was unacceptable.
Det Insp Ray Morton, of Cleveland Police, said: "This will give drivers the reassurance of being able to collect a sample to put alongside other evidence to bring offenders to justice."
Nigel Winter, operations director for Stagecoach, added: "Although such incidents are rare, this sends a clear message that unacceptable behaviour that disrupts the comfort of our passengers will not be tolerated onboard our buses."