PKI in .net Program

I'm trying to access a UDDI registry server programmatically using
..net. The registry server is set to require client certificates. If I
access the registry through Internet Explorer, a window pops up asking
me to select a PKI certificate. However, if I try to access the
registry through a C# .net program, I'm not asked for a certificate -
the connection to the server just fails. Is there some way I can tell
the program to send my PKI certificate to the registry server?

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