The paper presents the in-house method of quantitative analysis of 85 B mRNA in Mycobacterium tuberculosis cultures coming from seeded biological material taken from tuberculosis patients. After the proper culture time, the total RNA was isolated. Than, a one-step QRT-PCR was performed. High specificity and sensitivity of the method was confirmed e.g. by participation in the Mycobacterium tuberculosis QC Proficiency Panel Programme (European Quality Control for Molecular Diagnostics, Glasgow, Scotland, UK).