header() and require()

Hi. In some of my files, I have a require statement to get some global stuff accessable. I also have some header() redirects. They don't work (they worked before I added the requires). I moved the require under one of the header()s and that one works now, but I can't move it under the other one because stuff has to happen before the redirect and it needs the required stuff. So my question is do require statements produce output that I can't see (which would make the redirects not work)? The files I'm requiring don't have any output, which is why I'm confused. Thanks. Jason