A Sussex Police officer has been arrested on suspicion of money-laundering and drugs offences and suspended from his post.
The arrest followed the seizure of 3kg (6.6lb) of cocaine during a drugs raid, a police spokesman said.
The force confirmed the officer, who has not been named, was bailed without charge, pending further inquiries.
He was questioned on suspicion of possession of cocaine with intent to supply in Brighton.
A police spokesman said: "We can confirm a serving Sussex Police officer has been arrested in Brighton as part of an ongoing criminal investigation.
"He has been interviewed and bailed without charge pending further inquiries. He is currently suspended from duty.
"It would be remiss of us to comment further as criminal proceedings in this case have commenced."
Three other men were arrested as part of the operation, officers said.
One of them, Darren Simpson, 41, from Peacehaven, near Brighton, was charged with possession of cocaine with intent to supply after he was stopped in his car.
He was remanded in custody and is due to face a committal hearing next month.
The other men were questioned and freed on bail while inquiries continue.