There was a thread on this topic with sample code last month, titled "Is form open by another user?". You should be able to find it with a search at http://groups.google.com

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Sue Mosher, Outlook MVP
Outlook and Exchange solutions at http://www.slipstick.com
Author of
Microsoft Outlook Programming: Jumpstart
for Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> is it possible to determine if a contact item is opend from an other user?
>
> I want to avoid the situation that two users make changes at a contact Item
> at the same time!
>
> Thx Martini