In a previous paper, it was reported that deltamethrin-medicated bath of domestic dogs had a strong killing effect against Ph. chinensis, and could also inhibit its blood sucking ability or cause its death shortly after blood sucking. The effect could last for 30 days to 114 days, and mostly for 2 months in the local area. Based on our previous study, three villages (Yongle, Yongfeng, Anle) and a town (Chengguan) were selected from the mountainous region with high incidence of visceral leishmaniasis in Nanping County, northern Sichuan for carrying out an extensive experiment of medicated bathing of domestic dogs, where there were 13 new infected cases in the year of 1991 before the experiment. During the sandfly season in 1992, two rounds of medicated bathing of dogs were conducted, the drug concentration used was 50 ppm. From September 1992 to August 1993, the number of new infected cases was 11 in the above mentioned three villages and a town. Another two rounds of medicated bathing of dogs had been conducted during the sandfly season in 1993. The results show that there was no new infection from September 1993 to October 1994 in the three villages and a town, indicating that through two years' consecutive extensive medicated bathing of dogs in the endemic areas, canine visceral leishmaniasis transmission had been significantly interrupted. The authors consider that in the mountainous region of southern Gansu and northern Sichuan where it has been difficult to treat dogs, it might be more practical to use deltamethrin bathing of dogs for interrupting the transmission of canine visceral leishmaniasis.