An improved variant of the popular double cross-polarization (DCP) experiment for heteronuclear dipolar re-coupling in solid-state NMR spectroscopy under magic-angle-spinning is introduced. By simple phase and amplitude modulation of the rf irradiation at the Hartman-Hahn sideband conditions, the new pulse sequence, dubbed iDCP, enables broadband excitation with the high efficiency of gamma-encoded coherence transfer. The efficiency and robustness of iDCP toward isotropic chemical shift variations and chemical shift anisotropies, in the order typically applying for the backbone atoms in uniformly C-13,N-15-labeled proteins, is demonstrated numerically and experimentally by N-15 to C-13 coherence transfer for N-15-labeled N-Ac-L-valyl-L-leucine and C-13,N-15-labeled-L-threonine. (C) 2003 Elsevier B.V. All rights reserved.