The authors describe how the value of a nuclear spin coupling const. JAX can be detd. very accurately by comparing 2 complementary 2-dimensional multiplets obtained with selective correlation NMR spectroscopy (soft-COSY) and with pure in-phase correlation spectroscopy. The convolution method of J. J. Titman and J. Keeler (1990) was adapted to compare soft-COSY and PICSY multiplets. Illustrative results on the L-proline residue in cyclo-(L-Pro1-L-Pro2-D-Pro3) are presented. [on SciFinder (R)]