In order to elucidate the translocation of the systemic insecticide, phosphamidon (2-chloro-2-diethylcar-bamoyl-1-methylvinyl dimethyl phosphate), treated to pine trees against pine gall midges (Thocodiplosis japonensis Uchida et Inouye), [vinyl, carbonyl-^(14)C] phosphamidon was implanted into the trunks of 10-years old pine trees. The upward movement rates of the chemical within Korean red pine (pinus densiflora Sieb et Zucc.) in July and Japanese black pine (Pinus trambergii Parl.) in December were ca. 10 ㎝/hr and 2 ㎝/hr, respectively. The radioactivity persisted up to 75 days after treatment at the insecticidal level throughout the whole tree in Korean red pine in July, whereas it did up to 150 days in Japanese black pine in December. The chemical was translocated up to the top at the insecticidal level within 3 days after treatment in July, whereas in December it was within 15 days. The translocation of the chemical was much dependent upon the meteorological factors, including relative humidity, precipitation, and the duration of sunshine.