Profiles of the Ha line in a very bright loop prominence associated with the great limb flare of February 10, 1956, show pronounced violet asymmetries. Despite the fact that the centers of different profiles, made at several points in the line on two different exposures, exhibit relative Doppler displacements as high as 0.8 A, the shapes of all the profiles can be accounted for by the superposition on the main Ha profile of an additional component centered between 1.5 and 2.0 A to the violet. The possibility is discussed that the asymmetry may have been caused by the presence of abnormal amounts of deuterium, presumably generated by nuclear reactions during the flare event. It is concluded that, although the evidence for deuterium is not conclusive, it would be extremely important to observe other similar flareassociated prominences in the future, with modern high-dispersion spectrographs. Observations should also be made simultaneously on at least one additional line of an element other than hydrogen, in order to eliminate velocity effects.