How to search all system ports in C#.Net... I have to list all ports names in the combobox, how to proceed with this...?? vinaya.kumar

I honestly have no idea. If nothing in the System.IO.Ports Namespace works, then I'd probably look at the registry. Apparently, the GUID for the ports class is {4D36E978-E325-11CE-BFC1-08002BE10318}, so you could use that as a kicking off point. Also, this PC has one COM port, and it's listed in the registry as HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\ACPI\PNP0501\1 I assume a second COM port would be listed as . . . \PNP0501\2 It's not perfect (I'm not sure how Win9X saves its port information), but it might be your best bet. NOTE: C/C++ documentation I found suggests you let the user type it in, then attempt to open it. If the open fails, you inform the user to type in a new port.