The effect of radioactive sulfur-35 on the growth and tissue respiration in rye, Secale cereale L., Seedlings were Studied in this investigation. The growth and respiration rate of the materials treated with the different intensities of radioactivity, represented by the different concentration (μc) of radioactive sulfur were shown similar effects in treated groups as those of Gamma-ray or X-ray irradiation on plant materials. However, in the groups of 0.1 μc and 0.4 μc S^(35)-solution, the growth and respiration rate were stimulated somewhat more clearly than in case of control. And the higher concentration groups, 1.6 μc, 6.4 μc. and 25.6 μc were depressed of the growth and tissue respiration rate. The present data could be explained on the basis that the higher concentration treatments with the radioactive isotope did produce injury to the plant metabolism generally, but the moderate treatment would stimulate to the plant growth and tissue respiration.