Betaseron as well as the other interferons can cause this. I have been dealing with WBC counts up and down since I started on Beta in April.

The results I got back yesterday were at 2.9 and my neuro is giving up on me being on the full dose and I will be going back down to a half dose starting today.

Sometimes when this happens, lowering the dose for a little while will stabilize the counts. For me, my counts are at the low end of normal as long as I stay on the half dose. My neuro wanted me to try one last time to go to the full dose since my counts had been stable for many months on the half dose.

I would call your neuro to see if you should try lowering your dose. (I think I read you were on Beta - sorry if I am wrong).