Wow, works wonderfully.  I recently moved from a non tick area to the hills in Tennessee, and as soon as it stopped snowing the ticks came out.  Even though I have my dog on vet prescribed once a month flea, tick, heartworm etc she still was coming in with TICKS.  Second day after I put this collar on her....no more ticks.  I do watch her closely for any adverse effects as other posters have mentioned, but all is good.  Love this collar!!!