We previously reported the short period cure rate of mebendazole (MBZ) treatment to strongyloidiasis. We are now reporting the long period cure rate of the treatment. The results were as follows: 1) The cure rate was 73.9% (17/23) in single use of MBZ (100 mg twice daily for 28 days). 2) The cure rate was 100.0% (22/22) in combination therapy (thiabendazole 500 mg three times a day for 5 days and after that, MBZ 100 mg twice daily for 9 days). Before we obtained the cure rate of 6 months after the treatment described above, we concluded that MBZ could be used for the treatment of strongyloides infection because of the lack of severe side effects and suitable intervals between courses would prevent liver injury. Thus, in this study, 47 patients were treated with 100 mg of MBZ twice a day for 5 days and this treatment was repeated 1, 3 and 4 weeks later on the same schedules (group 1). But because of liver injury, 13 patients were interrupted and moved to the 4th course (group 2). The following results were obtained: 1) Out of a total of 60 patients, the cure rate was 88.1% (52/59) after 2 courses, 92.3% (12/13) after 3 courses and 100.0% (46/46) after the 4 courses were finished. 2) Diarrhea (10.6%), arthralgia and lumbago (8.5%) were observed in group 1. No side effects were observed in group 2. 3) The incidence of liver injury occurred 48.9% (23/47) in group 1 and 30.8% (4/13) in group 2. 4) Positive rate of HTLV-I antibody was 40.0% (24/60).(ABSTRACT TRUNCATED AT 250 WORDS)