Wiltshire police have arrested three men and one woman on suspicion of supplying drugs following the death of a 20-year-old man in Warminster in the early hours of New Years Day.
The dead man, who lived locally, is not being named until his body has been formally identified.
A post mortem has been carried but further toxicology tests are needed to establish the cause of death which detectives believe was drugs-related.
Leading the investigation, Detective Chief Inspector Paul Howlett appealed to New Year revellers who were in the area of East Street, Warminster, between 0100(GMT) and 0230 to contact police.