Technical Abstract: Gamma interferon (IFN-gamma)-induced protein 10 (IP-10) has recently shown promise as a diagnostic biomarker of Mycobacterium tuberculosis infection of humans. The aim of the current study was to compare IP-10 and IFN-gamma responses upon Mycobacterium bovis infection in cattle using archived samples from two aerosol inoculation studies. In the first study (10**4 cfu M. bovis, n = 7), M. bovis purified protein derivative (PPDb)-specific IP-10 and IFN-gamma gene expression were detected as early as 29d after challenge. PPDb-specific IP-10 and IFN-gamma mRNA responses followed a similar pattern of expression over the course of this study and were highly correlated (r = 0.852). In the second study (10**5 cfu M. bovis, n = 5), IP-10 and IFN-gamma (protein) responses to mycobacterial antigens were compared following challenge. IFN-gamma responses to mycobacterial antigens were detected 29d after challenge and were sustained during the remainder of the study. IFN-gamma responses to mycobacterial antigens exceeded corresponding responses in non-stimulated cultures. IP-10 responses to mycobacterial antigens exceeded pre-infection responses at 7d, 29d and 63d after challenge. In contrast to IFN-gamma, IP-10 responses to mycobacterial antigens generally did not exceed respective responses in non-stimulated cultures. IP-10 responses to media alone and to mycobacterial antigens followed a similar pattern of response. Correlations between IP-10 and IFN-gamma (protein) responses were modest (r ˜ 0.50 – 0.65). Taken together, these findings do not support the use of IP-10 protein as a biomarker for bovine TB using the current testing protocol and reagents; however, mRNA-based assays may be considered for further analysis.