Abstract: In order to evaluate the usefulness of intracutaneous test (IT) in longitudinal sur-veillance of filariasis, two administrative villages selected from Queshan County, Henan Province of China, endemic for Wuchereria bancrofti, were surveyed in 1982, 1983 and 1987 respectively. by IT with antigen FPT derived from Dirofilaria immitis.The result showed that the original level of IT to antigen FPT in the population was consistent with the data of either etiological or entomological investigation before chemotherapy. When the microfilaraemia rate and naturall filarial infection rate of mos-quitoes in a village were high, the positive rate and frequency of strong positivity (skin wheel diamater≥1.3mm) for immediate hypersensitivity reaction would be high too; and the reverse was true. It is suggested that both criteria of IT mentioned above may be useful in assessing endemicity of lymphatic filariasis before mass chemotherapy.The speed of negative conversion of IT in both groups, the previously microfilarae-mic patients and the amicrofilaraemic inhabitants positive to immediate hypersensitivity reaction before chemotherapy, were different, the former being significantly slower than that of the latter after mass and selective chemotherapy with diethylcarbamazine.AU of the three criteria for immediate hypersensitivity, positive rate, frequency of strong positivity and positive conversion rate, decreased gradually after a mass and selective DEC treatment. Until 1987, the 5th year after the chemotherapy, the average positive rate in the two villages dropped to 20.0% from 55.4% in 1982, the frequency of strong positivity to 2.8% from 23.8% in 1982, and the positive conversion rate to 9.7% (1984-1987) form 19.2% (1982-1983). This result indicated that the three criteria of IT reflect not only the status but also the trend of filariasis transmission after chemotherapy in an endemic area, and may be also useful in longitudinal seroepidemiological surveillance of lymphatic filariasis.