Feline idiopathic inflammatory bowel disease (IBD) is a common diagnosis in cats with chronic vomiting, diarrhea, and/or weight loss. The exact cause is unknown, but excessive inflammation in the gastrointestinal tract (GIT) resulting from genetic abnormalities, or loss of tolerance to normal bacteria are possible triggers. Current therapies include novel diets, antibiotics, and drugs that suppress the immune system. Probiotics are increasingly popular for the treatment of IBD. Lactobacillus acidophilus NCK2025 is an exciting probiotic candidate IBD therapy. Our goal is to investigate its immune effects on the GIT, persistence in the host, and potential adverse effects. Goals of this study include: demonstrating the ability of L. acidophilus NCK2025 to colonize the feline GIT, documenting induced synthesis of IL-10 by the GIT in response to the bacterium, and documenting the absence of adverse effects or induction of an undesirable immune response. The clinical relevance of this study is the potential to develop a new, effective therapy for feline idiopathic inflammatory bowel disease.