A new reagent for a skin test given the name Diaskintest has been designed for the screening diagnosis of tuberculosis and preclinical and clinical trials conducted. Preclinical trials were carried out on 315 laboratory animals (guinea-pigs, albino mice). The reagent Diaskintest was ascertained to be nontoxic, to have no sensitizing properties, to be safe and specific, and to induce no positive reactions in BCG-vaccinated animals and healthy guinea-pigs. Its specific activity was comparable with that of the national reference--purified tuberculin PPD-L-2. With progression of tuberculous lesions, the guinea-pigs showed higher responses to Diaskintest dilution and the BCG-vaccinated animals lacked responses to Diaskintest with increased delayed type hypersensitivity. The clinical trial was permitted by the Federal Service for Surveillance in Health Care and Social Development of the Russian Federation. Clinical trials were conducted in 150 persons. The safety, specificity, sensitivity of Diaskintest were first examined in the clinical studies and its action was compared with the results of tuberculin skin test (Mantoux test) with 2 TE of PPD L-2. Diaskintest was ascertained to be highly sensitive when given in a dose of 0.2 microg in 0.1 ml. In patients with active tuberculosis and new cases of Mycobacterium tuberculosis infection, the agent induced a positive skin reaction (a papule of more than 10 mm) in 98-100% of cases (p < 0.05). The agent caused no reaction associated with BCG vaccination. The specificity of the test was 93-100% with 95% significance. The rate of overexuberant reactions (vesicular necrotic changes, lymphangitis, and lymphadenitis) was 4-14% with 95% significance. Tuberculosis patients with significant immunopathological disorders might have no skin sensitivity to Diaskintest, as to PPD L-2 (a negative test). The findings substantiate the use of Diaskintest for mass epidemiological surveys for the differential diagnosis of tuberculosis and BCG vaccination-associated complications. The agent may be also used to evaluate the activity of the process in patients with tuberculosis and the efficiency of treatment in combination with other methods and to make a differential diagnosis of tuberculosis.