New X-ray and energetically optimal models of poly(dA):poly(dT) with the hydration spine in the minor groove have been compared with the NMR data in solution (Behling, R.W. and Kearns, D.R. (1986) Biochemistry 25, 3335-3346). These models have been refined to achieve a better fit with the NMR data. The obtained results suggest that the poly(dA):poly(dT) structure in a condensed state is similar to that in solution. The proposed conformations of poly(dA):poly(dT), unlike the classic B form, satisfy virtually all geometrical requirements which follow from the NMR data. Thus, the X-ray and energetically optimal poly(dA):poly(dT) structures (or those with slight modifications) can be considered as credible models of the poly(dA):poly(dT) double helix in solution. One of the features distinguishing these models from the classic B form is a narrowed minor groove.