Interferon gamma, known by its effects which enhance the bactericidal activity of macrophages on mycobacteria, is a lymphokine released from the T lymphocytes. The purpose of this prospective study was to test the role of interferon gamma levels in the diagnosis of tuberculous pleurisy. A total of 35 patients 14 of whom had tuberculous pleurisy were enrolled in the study. Diagnoses of the patients with tuberculous pleurisy were all confirmed by histopathology. Levels of interferon gamma were measured by using the QuantiFERON-TB(QFT) kit. Mean age in the tuberculous pleurisy group involving 4 females and 10 males was 37.4 (±18.3). The other group involving 21 patients included 14 patients with malignant pleurisy, 4 patients with parapneumonic pleurisy, and 3 patients with pleurisy transudate in character. This group consisted of 11 females and 10 males, the mean age being 59.1 (±14.9). Interferon gamma was detected to be positive in 9 of the patients with tuberculous pleurisy, and negative in the remaining 5 patients while the other group had 21 patients with negative results. In patients with tuberculous pleurisy, the sensitivity and specificity of gamma interferon positiveness were detected as being 64.3% and 100 %, respectively. The positive predictive value of the test positivity was 100 %, and the negative predictive value was 80.7 % as well. Despite the inadequate number of patients enrolled in this study, it was concluded that measurement of interferon gamma levels may well contribute to the diagnosis of tuberculous pleurisy.