In response to concerns over a disproportionate number of Crohn's disease cases within a animal diagnostic laboratory which employed bench-top handling of M. paratuberculosis sera was obtained from all 41 state and federal employees of the laboratory and matched with 168 sera obtained from random screening of human health care workers. Sera were examined by a modified ELISA using a PPD antigen prepared from a human isolate of M. paratuberculosis. a significantly higher level of antibodies was detected in the animal health workers as compared to controls (p=0.0009). Sera from the control human health population had a mean O_D410 of 0.29±0.10. In contrast, sera from the animal laboratory population had a mean OD₄₁₀ of 0.44±0.13 (p=0.0009 as compared to controls). Mean OD values of individual animal health employee categories were as follows: bacteriologists engaged in M. paratuberculosis culture, 0.56±0.08 (p=0.0026); field, 0.46±0.16 (p=0.0009); general laboratory workers not involved in M. paratuberculosis culture, 0.41±0.11 (p=0.0001), and necropsy, 0.40±0.13 (p=ns). Differences in statistical significance of the animal health workers as compared to controls reflect the number of employees in each category; therefore, statistical significance was not suggested with those employees performing necropsy (n=3) even though OD values were similar to those in other groups. There was no significant difference between the individual groups of animal health employees. Of the 3 employees having direct daily contact with M. paratuberculosis, 2 had elevated OD reading of 0.58 and 0.67, and the third employee a reading of 0.49 which was equal to 2 SD above the mean of controls. The continued practice of bench-top handling of M. paratuberculosis should be discouraged.