Proton-coupled 13C NMR spectra were studied by a technique which involves Fourier transformation of spin echo modulation. When the protons are strongly coupled, the \"proton flip\" version of this expt. generates a new form of 13C spectrum which is quite distinct from the multiplet structure of the conventional NMR spectrum. The transition frequencies and intensities are exactly sym. about the center frequency and some lines have neg. intensities. Exptl. spectra from the C2 site in pyridine are presented and analyzed by means of an iterative program derived from LAOCOON III. The resulting proton-C coupling consts. are in excellent agreement with those obtained by anal. of the conventional spectrum. The new program may also be used to calc. the echo modulation in strongly coupled homonuclear spin systems, and the echo modulation induced in heteronuclear systems by strongly nonresonant spins. [on SciFinder (R)]