Response of Hordeum vulgare L. cv. Zafer-160 mature embryos to copper toxicity was evaluated under in vitro conditions. Mature embryos of barley were cultured on Murashige and Skoog medium supplemented with different concentrations of copper sulphate (CuSO4) 0-1600 mu M. The number of germinating embryos was recorded during 20 days following inoculation. Plant growth was strongly reduced with high concentrations of copper. Germination rate was 95% for control while 30% for 1600 mu M copper treated plants. Total soluble protein content and peroxidase activity were determined spectrophotometrically. Total protein content decreased; however, no significant change in guaiacol peroxidase activity was observed between control and 1600 mu M copper treated shoots. Copper accumulation is correlated with copper concentrations and higher accumulation was observed in roots compared to shoots.