Haptoglobin (Hp) serum concentration is a highly sensitive, non-specific indicator of inflammation. In the present study, following the example of studies conducted on humans, we analysed whether haptoglobin concentrations in pleural fluids and sera in tuberculin-reactor cattle could be an additional biomarker of Mycobacterium bovis infection. The clinical material (serum, n = 60, pleural fluid, n = 80) was collected from 140 dairy cattle (Bos taurus) shortly before culling at slaughter. During postmortem examination, organs were assessed for tuberculosis-like lesions and tissue samples were collected from all animals post-mortem for Mycobacterium tuberculosis complex (MTBC) culture. The relationship of Hp serum concentrations in cattle with and without tuberculous and the results of MTBC culture were analysed. Serum samples showed a positive correlation between the Hp concentrations and MTBC culture. However, this phenomenon was not confirmed in pleural fluids. Thus, Hp concentrations in cattle serum can be a useful complementary tuberculosis diagnostic tool in cattle.