Observations are reported of resolved components of deuterium Balmer emission in neutral beam heated JET plasmas. The features are interpreted as Doppler shifted emission from deuterium in the neutral beams spectrally resolved into components by the V x B motional Stark electric field. The mechanisms of excitation of the deuterium are elucidated and the emission modelled. Attention is drawn to the diagnostic potential of the observations for measurement of local magnetic fields, deuteron density and effective plasma ion charge.