The positron emitters11C,13N and18F and their labeled compounds have been produced for studies on plants using a newly developed positron emitting tracer imaging system. Although this system covers, at present, a limited area in a plant, the distribution of the positron emitter fed into the plant can be visualized dynamically. Further development of positron-emitter-labeled compounds is expected to elucidate the physiological function of plants in vivo.