The first detection and identification of deuterium Balmer lines were recently reported in H ii regions, using high spectral resolution data secured at CFHT and VLT. The Di lines appear as faint, narrow emission features in the blue wings of the H i Balmer lines and can be distinguished from high-velocity Hi emission. The identification as deuterium and the excitation mechanism as fluorescence are both established beyond doubt. The deuterium Balmer series might lead to a new, optical method of deuterium abundance measurement in the interstellar medium. This may be the only way to observe atomic deuterium in objects like the Magellanic Clouds or low metallicity blue compact galaxies.