A variation on correlation spectroscopy (COSY), the two-dimensional NMR technique for correlation of the chemical shifts of two paramagnetic nuclei, which gives much sharper linewidths than COSY and which thus extends the usefulness of the method to much larger macromolecules. Decreased linewidth is achieved by omission of the decoupling step of COSY, in which the four peaks which arise from ¹⁵N-¹H or ¹³C-¹H interactions are combined to preserve their intensities at the cost of sharpness of linewidth; in TROSY, only the strongest peak of the four is selected.