Tritrichomonas foetus is a parasite that has been identified as an important cause of diarrhea in domestic cats. Infection with T. foetus is characterized by a waxing and waning large bowel diarrhea that occasionally contains fresh blood and mucus. The prevalence of T. foetus infection at an international cat show was found to be 31% (36 out of 117 cats), with 28 out of 89 catteries affected. Risk factors for protozoal shedding and exacerbation of diarrhea included concurrent infection with Cryptosporidium spp., and cats living in close proximity with one another. There is currently no therapy for elimination of the organism and cats may shed protozoa continually in spite of feces returning to normal consistency. A recent report showed that 57% of cats diagnosed with T. foetus-associated diarrhea were still shedding the organism up to 3 years following diagnosis, and diarrhea persisted for up to 2 years in many cats, despite aggressive antimicrobial administration. Cats infected with T. foetus have failed treatment with recommended and higher dosages of conventional antimicrobial drugs, including metronidazole, fenbendazole, sulfadimethoxine, furazolidone, tylosin, amoxicillin, and paromomycin. The goal of this study is to evaluate the in vitro susceptibility of feline T. foetus strains to conventional and novel antimicrobial agents in an effort to find a safe and efficacious treatment for elimination of the organism. The novel compounds that will be studied have already demonstrated excellent efficacy in vitro against T. foetus strains isolated from cattle.