For the muon spectrometer of the ATLAS detector at the Large Hadron
Collider (LHC) an area of 5500 m^2 has to be covered with high-precision drift
chambers consisting of three or four layers of pressurised drift tubes on either 
side of a space frame carrying an optical monitoring system to correct for
deformations (Monitored Drift Tube chambers, MDT). A full-scale prototype of a large
MDT chamber with 432 drift tubes of 3.8 m length has been extensively tested.
With X-ray measurements at CERN the positioning accuracy of the signal wires 
in the chamber was shown to be better than the required 20 micrometer rms. 
The average position resolution of the drift tubes in the chamber was measured
in a test beam at CERN to be 70 micrometer rms with an Ar:CO_2 (93:7) gas mixture at 3 bar
selected to avoid aging of the chambers under LHC conditions. The series production
of MDT chambers for ATLAS is just starting. Extensive tests are performed
on individual drift tubes and on the completed chambers. We report about the first 
results and experience.