Specific-heat data on Ni(C 5H 5NO) 6(ClO 4) 2 are presented for fields 0 ⩽ H ⩽ 60 kOe and temperatures 0.1 ⩽ T ⩽ 1.3 K. In this material the S = 1 ground triplet is split by a trigonal crystal field term into a singlet and a higher lying doublet, such that ordering cannot occur in zero field. The field-induced magnetic phase transitions are studied both experimentally and theoretically, using molecular field theory, high-temperature series expansions and spin-wave theory. We obtain the values J/ k = -(0.20 ± 0.01) K and D/ k = 6.6 ± 0.2 K for the antiferromagnetic (subcritical) exchange constant and for the crystal-field splitting parameter, respectively.