The other poster is correct about the COMLEX being more clinical. There is also less biochem on COMLEX and a ton of biochem AND molecular bio on the USMLE. There is more anatomy on COMLEX and some of these questions are tied into OMM questions. There also seems to be more micro on the COMLEX. You will find more graphs and charts on the USMLE. Both tests are quite different, but since COMLEX will be going computer based soon it will be interesting to see how the test changes.