I am using the ThreadPool to queue 1000\'s of workitems
While(reading in data for processing)
{
args = some data that has been read;
ThreadPool.Queue
I don't think there is a built-in way, but you can introduce a [static?] counter that would increase/decrease; for that you would have to create your own method that would wrap ThreadPool.QueueUserWorkItem() and take care of the counter.
By the way, just in case you are running .NET 4.0, you should use TaskFactory.StartNew instead of ThreadPool.QueueUserWorkItem() - it's said to have better memory/thread management.