The mini DNA kits are being used to help police track down anyone who spits at drivers or passengers.
So far this year, 50 spitting incidents towards a member of staff have been reported in the West Midlands.
The kits – which feature swabs, gloves and sealed bags – allow staff to take saliva samples and protect them from contamination before sending them for forensic analysis.
Pc Shaun Hickinbottom, the investigation officer for Safer Travel said: “Spitting is a disgusting, despicable offence. Drivers and passengers should not be expected to tolerate it on our bus routes.
“Spitting at someone leaves a trail of DNA behind and these spit kit devises allows us to obtain irrefutable DNA evidence which help us track down offenders and secure convictions at court.
“This is a criminal offence and we will deal with this seriously. We have had cases of offenders being handed short jail sentences after spitting at passengers or bus staff.”
A National Express spokesman said the DNA samples were invaluable in tracking down offenders and would be kept on the database for future reference.
Earlier this year a driver was forced to speak to a number of rowdy teenagers on the bus about their behaviour. One of the teenagers spat in the driver’s face before getting off the bus.
Spit samples were taken from the driver’s clothes and the steering wheel and sent off for forensic analysis. The DNA was compared with over six million DNA profiles on the National Database, but there was no match.
Two months later, a 13-year-old boy was arrested for an unrelated incident and the DNA was found to match.
In March this year, a 33-year-old man spat at a bus driver and ran off. DNA samples were taken from the driver’s arm and trousers and resulted in the offender being jailed for 35 weeks and fined £150.
Tom Stables, Managing Director of National Express West Midlands, said: "My staff have the absolute right to work without being spat on. We will pursue anyone who is guilty of this revolting behaviour. These DNA kits mean we can help Safer Travel Police track these people down, stop them and make sure they face justice."
The Safer Travel Partnership stressed that spitting would be dealt with as a criminal offence, but also urged passengers to help tackle non-criminal nuisance behaviour by using the See Something Say Something campaign.
Passengers who witness anti-social behaviour during their journey can say something anonymously by texting the word ‘bus’, ‘metro’ or ‘rail’ followed by a space and then details of the incident including time, date, location and route number to 83010.