The applicability of Mycobacterium tuberculosis-gene-amplification test (NAT) in breath condensate (BC) was examined in lung tuberculosis (TB). Ten patients with bacteriologically confirmed lung TB have been examined by ligase chain reaction (LCx). In BC the NAT were negative in all patients as well as the examination of acid fast smears and of solid phase or liquid media cultures were. This indicates that the use of NAT in BC can not replace or complement sputum or materials obtained invasively in patients with lung TB.