Spin indices of some simple nitrenes (R-N) and phosphinidenes (R-P), in both lowest-lying singlet and triplet states. have been evaluated using density functional computations at the B3LYP/6-311+G(d,p) level. Relatively good correlations between the spin hardness, spin-philicity and spin-donicity, and the vertical singlet-triplet energy gaps have been established. A comparison with spin indices of related reactive intermediates such as carbenes, silylenes and germylenes allows their similarities and differences to be emphasized. (C) 2004 Elsevier B.V. All rights reserved.