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During the last years the study of the influence of the dislocation density on electrical and optical properties of semiconductors received an increasing interest, The appearance of bound states connected with dislocations is expected.Some theoretical aspects of this problem a r e discussed by Emtage (1). Auleytner, Gross et al. (2) found a shift of the spectrum of anomalous crystals to short wavelengths. The authors supposed that dislocations forming small-angle boundaries cause this shift. It must be noted that the dislocations investigated in paper (2).which are formed during the process of crystal growth, can differ in their properties from dislocations introduced by plastic flow. Therefore the investigation of the spectrum of plastically deformed crystals is important.The experiment presented here is an attempt to determine the dependence of the optical spectra of CdS single crystals near the absorption edge on the density of dislocations which were introduced into the crystals by plastic flow. The samples used for deformation were cut from massive single crystals. The shape and orientation of the samples is shown in Fig. l a , b. Two orientations were chosen to realize the flow on the different slip planes. Deformation was performed by uniaxial strain of the samples at 100 C. The strain rate was 5 pm/min. The initial 4 -2 9 -2 dislocation density was about 10 cm . The maximum final density was 10 cm , a s measured by transmission electron microscopy. The reflection and fluorescence spectra of the samples with different dislocation density were measured at 77 and 4.2 OK. The absorption spectra of thick crystals were measured at 290 and 77 K.The following results were obtained:1. The absorption edge becomes rather diffuse with increasing dislocation density. 0The temperature shift of the absorption edge of deformed crystals was a little smaller than that of non-deformed ones.