Dispersed detonation nanodiamonds have been studied by continuous-wave (CW) and pulse EPR techniques. The spectrum of bulk radicals (g = 2.0025 +/- 0.0002, a Lorentz line shape with Delta H-pp = 0.95 +/- 0.05 mT) dominated in CW EPR and prevented to record spectra from other paramagnetic species. The pulse EPR-spectrum was the superposition of the distorted P1-center spectrum with parameters (g = 2.0025, A(xx) = 2.57 mT, A(yy) = 3.08 mT, A(zz) = 4.07 mT), the H1-center spectrum (g = 2.0028) and the single line (g = 2.0025, DHpp = 0.40 +/- 0.05 mT) from other centers which may be assigned to surface radicals. The concentration of P1-centers has been estimated by CW EPR as 2 +/- 1 ppm N. (C) 2010 Elsevier B. V. All rights reserved.