Volumes of secure messages being sent between users of Global Health's ReferralNet system and Telstra Health's Argus have been increasing by 12 per cent per month on average since two-way interoperability was achieved in February last year, the vendors report.

The numbers are particularly strong in Victoria, where both Argus and ReferralNet have a large market share, and involve users such as GPs, allied health professionals and several local hospitals with several thousand messages being exchanged each month.