Two Victorian men have been charged with drug trafficking after South Australian police allegedly discovered a large quantity of drugs during a vehicle search in the state's south-east.

Police stopped a hire car on the Dukes Highway near Bordertown last week as part of an investigation. During the search, officers allegedly located approximately 12.5 kilograms of cannabis, including 250 grams of methamphetamine.

The two men, aged 24 and 39, were arrested following the discovery and subsequently charged with trafficking a large commercial quantity of a controlled substance.

Police allege the drugs were being transported in the vehicle. The seizure is now part of an ongoing investigation into suspected drug trafficking activity in the region.

The arrest occurred near Bordertown, a regional South Australian town close to the Victorian border. The Dukes Highway is a major transport route connecting South Australia and Victoria, making the area an important corridor for traffic travelling between the two states.

Following their arrests, both men were refused bail and remanded in custody. They are due to remain in custody until June next year, when the matter is scheduled to return to court.

The quantity of cannabis allegedly discovered during the vehicle search was substantial, while the methamphetamine seizure added another serious element to the charges.

Drug trafficking offences involving commercial quantities can carry significant penalties under South Australian law. However, the allegations against the two men have not been tested in court, and both remain entitled to the presumption of innocence unless proven guilty.

Police have not indicated whether additional people are being investigated in connection with the alleged drug transportation. Further inquiries may be conducted as investigators examine the source of the drugs, their intended destination and the circumstances surrounding their transport.

The seizure demonstrates the role of roadside and highway policing in detecting suspected drug transportation across regional areas. The Dukes Highway provides a major connection between Adelaide, the South Australian south-east and western Victoria.

Authorities continue to investigate suspected organised drug activity across transport routes linking the two states. Vehicle searches can form part of broader investigations where police receive information about suspected trafficking or identify circumstances requiring further examination.

The two men will face further court proceedings as the case progresses.

Police have not publicly released information identifying the alleged intended recipients of the drugs or the circumstances that led officers to search the hire car.

The investigation remains ongoing, and further charges are possible depending on the outcome of police inquiries.