The objective of this study was to determine whether orally ingested M. paratuberculosis could cause a "false" positive fecal culture result in uninfected cattle. Six uninfected Guernsey heifers (age 2 years) were given feces from a heavily infected cow with clinical signs of paratuberculosis. Each pair received one of three doses (2 ml feces/kg body weight, 0.5 ml/kg, or 0.12 ml/kg) by orogastric tube. Feces were collected three times daily and cultured for M. paratuberculosis on Herrold's egg yolk medium using the centrifugation technique. Intradermal johnin tests were performed prior to and 14 days after the dosing. Serum was collected for ELISA testing (LAM antigen) prior to and 7 and 14 days after dosing. All heifers had detectable M. paratuberculosis organisms in feces within 24 hours of treatment, and cultures remained positive for up to 6 days. The concentration of M. paratuberculosis organisms in the feces was approximately proportional to the dosage of infected feces given. Results of intradermal johnin testing and serum ELISA testing remained negative throughout the experiment. The heifers were given the same dose a second time, 14 days after the first dose, with similar results. Two weeks following the second dose, (28 days after the first dose), the heifers were slaughtered and ileum and mesenteric lymph nodes collected for mycobacterial culturing and histopathology. All lymph nodes were culture-negative but ileum samples were culture-positive. Histopathology revealed mild eosinophilic inflammation in the mesenteric lymph nodes and no acid fast staining organisms. Ingestion of feces from an infected cow can apparently result in a positive fecal culture test result in uninfected cattle.