2D 31P/1H correlation spectroscopy has been used to assign individual phosphates in the self-complementary DNA fragment d(CGTACG), which is present in solution as a B-DNA type double helix. 31P chemical shift variation with temperature and with the base sequence has been studied, and evidence is given of a steric clash between purines in the minor groove, affecting the chemical shift of the innermost TpA phosphate. For this hexanucleotide there is a good correlation of "P shifts with both the helical twist (C,) and roll angle (Z2) Calladine-Dickerson sum functions. Different types of linear correlations, also including data from other nucleotides, have been performed. The results show that it is more appropriate to consider the change in chemical shifts as it occurs during melting rather than the actual "P shifts. An interesting correlation was also found between "P chemical shifts and P,H-3' coupling constants.