It is well known that treatment of Chlamydia pneumoniae infections is
difficult. High doses and prolonged treatment is often needed to achie
ve clinical cure despite good in vitro effect of the drugs used, We he
re discuss different methodological problems in the determination of M
IC and MBC values of C. pneumoniae. The length of the preincubation ti
me and the lack of fluctuation of the antibiotic concentrations may af
fect the outcome of the currently used assay.