Why are OPTIONS requests not arriving in my ASP.NET application?

I can’t seem to receive HTTP OPTIONS requests in my IIS6 hosted ASP.NET application. I’m testing it using a debug breakpoint (and file-log) in my Global.asax‘s Application_BeginRequest method. The breakpoint is never hit and the client gets a HTTP 403 Forbidden, I’m assuming from IIS6 directly (GETs and POSTs work fine btw).