I am SO HAPPY I came upon this web site. I had no idea that Hartz had such a reputation, I thought I had an isolated incident. I was contemplating purchasing Frontline or Hartz, actually I was looking up the active ingredients, and I am positive I will never buy Hartz again. A few months ago, I gave my 4 cats Hartz drops (I got the right one, with their weight, etc.). The next day, 3 of my cats hardly moved, they acted mad at me, while my 4th started having tremors. I couldn’t even believe that I had done that to my cats. Fortunately, the 3 cats recovered quickly…after a day or so, but the 4th cat had burn like wounds on her neck where it was applied, and she suffered tremors, unable to walk for 4 days. I called the vet, he helped me through it. I just thought it affected her more because she was older (8 yrs old), and I knew I would never give it to her again, but thanks to all of you and this web site, none of my animals will ever get it, nor will my friends. Thanks for saving my animals lives….