I.r. spectra of solid N2H2 and N2D2 have been measured from 600–4000 cm–1 at liquid nitrogen temperature. For both compounds five bands have been observed and tentatively assigned to the three allowed fundamentals and to two combination bands of trans-di-imide. The assignments were made by comparison with the gas-phase spectrum of N2H2, with existing data of similar molecules, and on the basis of the isotopic effect.