Heteronuclear aipolar decoupling in MAS solid state NMR studies of biological systems has been investigated at moderate spinning speeds. It is shown that the efficacy of CNnv symmetry-based decoupling schemes with tanh/tan adiabatic pulses can be significantly improved by optimising the amplitude and frequency modulation characteristics of the inversion pulses employed. The decoupling performance of the symmetry-based schemes is compared with that of the commonly used TPPM technique. (c) 2006 Elsevier B.V. All rights reserved.