The effect of exogenous hydrogen peroxide (H2O2) on mitotic activity and chromosomal aberrations in root tip meristems of barley (Hordeum vulgare L. var. Tokak 157/37) germinated under salinity was analyzed. The inhibitory effect of salinity on mitotic index and the frequency of chromosomal aberrations increased with increasing salt concentration (0.00 control, 0.35, 0.40, 0.45 M, molal NaCl). The frequency of chromosomal aberrations of seeds germinated in medium with 0.40 M NaCl after pretreatment with H2O2 (30 mu M, micromolal) was significantly higher than the control group. The highest concentration of NaCl (0.45 M) together with H2O2 caused total inhibition of germination. In this study, the intention was to determine the performance of H2O2 in alleviating detrimental effect of salt stress on mitotic activity and chromosomal aberrations. However, H2O2 did not reduce the detrimental effect of NaCl on these parameters. Also, it caused higher chromotoxic effect compared to those of control groups.