Elimination of microfilaria in dogs infected with zoonotic Dirofilaria repens would be desirable to reduce further spread. Moxidectin has demonstrated efficacy against microfilariae and safety in dogs infected with Dirofilaria immitis and could be an option for controlling D. repens microfilariae. A field study with 64 dogs previously confirmed positive for D. repens microfilaria was conducted in Hungary, in which a spot-on product (Advocate, Bayer) was tested. Treatments were applied to 44 dogs once a month for 3 months (five dogs) or 6 months (22 dogs), alternatively every 2 weeks for 6 months (17 dogs). Twenty dogs remained untreated. Microfilaria counts were performed once a month and for a further 6 months following the last treatment. Two weeks after the first treatment, 38 of 44 dogs were microfilaria negative. Four weeks after the initial treatment, one dog still showed a low microfilaria count. Following the second treatment, all treated dogs were negative. This status was maintained during the 6-month observation period after the last treatment. These data demonstrate the successful long-lasting elimination of microfilariae. Moreover, it may be supposed that adult D. repens were killed based on the observation that no further microfilariae were seen up to 6 months after the end of the treatment period.