From August to October 1994, a field trial of preventive treatment with artemether (Art) was carried out in Minglang District of Yiyang City, Hunan Province, an islet with embankment type endemic area nearby southern Donting Lake region. The residents who frequently contacted with the infested water were selected for study and allocated to the Art group and the control group in reference to paired methods of randomization table. About one month before administration of Art, all residents under study were examined by stool hatching technique after nylon-bag concentration to determine the infection rate of each group, and then treated with praziquantel at a single dose of 40 mg/kg in stool egg-negative residents and 50 mg/kg in stool egg-positive ones. In Art group, the first dose of 6 mg/kg was given in late August, followed by repeated dosing every 15 days for 3 times. Placebo (starch) was given to the study residents in the control group at the same time as in Art group. The efficacy was evaluated by stool examination 25-32 days after the last medication. The results showed that after the preventive administration of Art, 20 out of 365 study residents in Art group revealed stool positive with an infection rate of 5.5%, while in the control group 51 out of 376 study residents showed stool positive with an infection rate of 13.6%. The difference between the two groups was statistically significant. Meantime, two cases of acute schistosomiasis were seen in the control group, but none was observed in Art group. The egg per gram of feces (EPG) determined with the Kato-Katz method was 122 +/- 79 (range 12-192) in Art group and 681 +/- 909 (range 12-2,760) in the control group. No apparent adverse side effect was seen during the treatment with Art, and no abnormal change in liver and renal function was detected after the last medication. The preliminary study indicates that application of the preventive administration of Art in the endemic area during the transmission season may effectively reduce both the infection rate and intensity of schistosomiasis.