The experiment was conducted, in Nagara-cho, Chiba Prefecture in 1979, to confirm the occurrence of dwarfing symptom of rice plant in paddy field sprayed with benthiocarb herbicide.<br>1. Benthiocarb was first applied on May 4th, immediately after the transplanting, and the second application of benthiocarb was made 25 days after the transplantation. The dwarfing symptom appeared in 30 to 35 days after the first treatment, and the symptom developed remarkably in 45 to 56 days after the treatment. Thereafter, the growth of rice was fairly recovered. Leaf dying due to simetryne application was also observed at the early stage of dwarfing symptom.<br>2. The dwarfing symptom was not observed both in control plots and in the plots where benthiocarb herbicide was applied, for the first time, 25 days after the transplanting. In all the plots where benthiocarb was applied immediately after the transplantation, the dwarfing symptom of rice was observed with difference in degree of state among the plots. The dwarfing symptom occurred notably in the plots of vast volume application, and in case the same amount of benthiocarb was applied, the dwarfing symptom occurred notably in the plots where fresh rice straw was incorporated in autumn of previous year.<br>3. The plant height of rice with dwarfing symptom was below the normal height. Rice plants developed two types of abnormal symptoms: (a) dwarf plant with increased number of tillerings, (b) dwarf plant with retarded number of tillerings. In the former case, the number of ears on the main stem was decreased and the tillering from 4 to 7th nodal position in the primary tiller was retarded. However, the primary tiller from above the 8th nodal position and also, the secondary tiller increased.<br>4. Yield of rice was decreased remarkably when the dwarfing symptom occurred severely. The decrease of yield was caused by the decrease of number of spikelets per ear and lowering of percentage of ripened grains. In case of remarkable leaf dying, decrease of number of ears caused the decrease of yield.<br>5. The oxidation-reduction potential in the soil was reduced remarkably 25 days after the transplanting. The degree of reduction was lowest in the incorporation plot of fresh rice straw in autumn, followed by spring incorporation plot, then non-incorporation plot. The difference among the three plots was small.