i may be wrong. but I think many people mix the USMLE CD of 150 released questions as the NBME released, which I guess they are. So there is only one set of 150 q, ...you can call it NBME or USMLE, it's the same questions. HOWEVER, there are NBME practice questions from the NBME site which are $45 bucks a test. You should use them towards the end of your studies to guage where you stand, ..if you are ready, or if you should delay. Supposedly they are fairly accurate predictor of Step 1 score. I hope that helps... 😎