The exptl. verification of offset profiles and calibration of selective pulses in NMR is usually carried out with doped water samples but not under conditions typical of macromols. with short T2, long T1, and possibly homo- and heteronuclear couplings. A new method for selective excitation in isotopically labeled macromols. is shown to be particularly suited to this purpose. This is illustrated for a backbone amide resonance in a sample of 15N-labeled human ubiquitin. (c) 1999 Academic Press. [on SciFinder (R)]