The Canadian company which makes BlackBerry smartphones has agreed to hand over user codes which will let Saudi authorities monitor BlackBerry Messenger activity.
It is the latest stage in Research In Motion's bid to stop the kingdom from silencing the messaging service following concerns about a possible threat to security.
BlackBerry Messenger is popular with young singles in Saudi Arabia, an Islamic society where contact between unrelated men and women is restricted.
Saudi Arabia, like United Arab Emirates, Kuwait, India and some other countries, has sought access to encrypted BlackBerry communications.
India's Ministry of Home Affairs has called the country's mobile phone providers for a meeting to discuss security concerns related to BlackBerry services.
A statement on BlackBerry's website says: "Security is the cornerstone of the BlackBerry solution, allowing users to confidently access sensitive information at all times."