In 2-dimensional correlation spectra of strongly coupled spin systems obtained with the z-filtered COSY technique, the amplitudes of cross and diagonal peaks obey simple rules. They are simply proportional to the product of the amplitudes of the corresponding lines in the conventional 1-dimensional spectra. The spectra obtained with the complementary anti-z-COSY method can be simulated with a program called Grandchild of Laocoon, which is based on an algorithm originally developed to describe J spectra of strongly coupled systems. Simulations can be calcd. for ?7 spins, but show interesting features even in ABX systems where, due to virtual coupling effects, cross peaks may occur between pairs of nuclei that are not coupled together. Theor. predictions with exptl. spectra of the dinucleotide 2'-deoxyadenylyl-(3' -> 5')-2'-deoxythymidine and the peptide cyclo-(L-Pro1-L-Pro2-D-Pro3). [on SciFinder (R)]