The theory of single-transition cross-polarization in NMR is presented and verified by exptl. evidence. In comparison to conventional cross-polarization a qual. change in the mechanism is obsd. Under the influence of matched radiofrequency fields with amplitudes that are smaller than the scalar coupling const. JIS for a two-spin system with I=(1)/(2) and S=(1)/(2) in isotropic soln., two simultaneous coherence transfer processes are obsd. between single-transition coherences which have phases that are parallel to those of the radiofrequency fields, an on-resonance transfer from SxIa to SaIx and an off-resonance transfer from SxIb to SbIx, without mixing between the two pathways. Coherence transfer is also obsd. between single-transition coherences with phases that are perpendicular to the radiofrequency fields, from SyIa to SaIy and from SyIb to SbIy, as well as between longitudinal components, from SzIa to SaIz and from SzIb to SbIz. The transfer may therefore be considered quasi-isotropic. The authors consider the conditions under which such transfer processes can be obsd. Coherence transfer is affected by differential relaxation due to cross-correlation effects. [on SciFinder (R)]