Three people from Sheffield have been arrested on suspicion of possessing heroin with intent to supply.
Two men, aged 22 and 26, and a 22-year-old woman were detained by officers from North Yorkshire Police who pulled over a blue VW Golf car in York at 5.20pm on Monday.
Officers believed they could smell cannabis, so carried out a search of the vehicle.
A large amount of uncut heroin was found and the car was seized.
Following questioning in custody, the three arrested were released on conditional police bail pending further enquiries.
Detectives are appealing for anyone with information that could assist the investigation to contact North Yorkshire Police on 101, select option two, and ask for York CID.