A continuous wave and pulse electron paramagnetic resonance study of the base-on form of cob(II)alamin diluted in hydroxocob(III)alamin powder is presented. HYSCORE spectroscopy at X- and Q-band was used to study the weakly coupled corrin nitrogens and the remote nitrogen of the axial dimethylbenzimidazole ligand. Simulations of the spectra measured at different field positions enabled the following parameters to be determined: for the corrin nitrogens the hyperfine principal values are A(1) = -4.5 MHz, A(2) = -3.4 MHz and A(3) = (-2.2 to -2.5) MHz with Euler angles [x, beta, gamma] = [n90, 25, 0]degrees and the nuclear quadrupole parameters are e(2)qQ/h = 1.75 MHz and n = 0.95 with Euler angles [x, beta, gamma] = [90 + n90, 90, 12.5]degrees , where eta = 0, 1, 2, 3. The remote nitrogen of the dimethylbenzimidazole ligand has A(1) = 1.75 MHz, A(2) = 1.75 MHz and A(3) = 2.10 MHz with Euler angles [x, beta, gamma] = [-45, -10, 0]degrees and e(2)qQ/h = -3.3 MHz and eta = 0.1 with Euler angles [x, beta, gamma] = [45, 90, 67]degrees (C) 2002 Elsevier Science B.V. All rights reserved.