Armed police were called to Beeston on Sunday after reports of what appeared to be a firearm in a car.
West Yorkshire Police received an anonymous call about a car in Greenmount Street at 6.17pm.
The car was traced to a property in Crossland Terrace, half a mile away.
Four men, aged 24 to 34, were arrested from the address on suspicion of firearms offences.
The property was searched and quantities of what were believed to cocaine, heroin and cannabis were found.
No firearm was found. The car was recovered for examination.
Those arrested were later released on police bail pending further enquiries.