The NEMA NU 2-2001 protocol has been especially designed for the performance evaluation of whole-body positron emission tomography (PET) measurements with scanners acquiring data in three-dimensional (3-D) mode without septa or with septa retracted. We report on the comparative NEMA NU 2-2001 performance tests on four different Siemens/CTI ECAT PET scanners, the two bismuth germanate oxide scanners HR+ and EXACT and the two lutetium oxyorthosilicate scanners ACCEL and EMERGE. All scanners were operated in 3-D mode only. Until now, no complete NEMA NU 2-2001 evaluations have been reported for the HR+ and EXACT. For the ACCEL and the EMERGE, these are the first published performance characteristics as far as we know. The HR+ showed a superior spatial resolution, whereas the ACCEL had the best countrate [noise equivalent count (NEC)] performance above a radioactivity concentration of 2 kBq/cc. The sensitivity of the full-ring scanners did not differ much with numbers between 5982 and 7180 cps/MBq. The sensitivity of the partial-ring scanner EMERGE was 2279 cps/MBq. Although the EMERGE yields lower NEC rates than the EXACT for radioactivity concentrations less than 10 kBq/cc, it is favorable beyond this cross over point. The scatter fraction of all four scanners was about 48%. The lesions to be examined by the image quality test could be seen best with the ACCEL. The NEMA NU 2-2001 performance tests proved to be a valuable guideline for this instrumental comparison.