The phenotypic properties of the M. tuberculosis strains obtained from patients with pulmonary or extra-pulmonary tuberculosis are determined by a complex set of factors: the genetic characteristics of the pathogen, its ability to adapt in vivo and in vitro, the influence of the host's immune system and chemotherapy. The growth rate as the phenotypic property is the most accessible for the study of the host-pathogen relationships at the level of host/strain population interactions. The aim of the study is to assess in vitro of the growth rate of M. tuberculosis strains isolated from patients with pulmonary and extra-pulmonary tuberculosis: untreated and treated (with surgical and non-surgical treatment) and also sensitive and resistant isolates in comparison with the reference strain H37Rv. To estimate the growth rate of 116 clinical isolates we have used the modified method originally developed by von Groll and co-authors: to get the bacteria growth curve the fluorescence intensity of growing strains (with indicator resazurin) has been measured daily for 8 days in 96-well plate. The growth rate is determined as the slope of the growth curve. The mean values of the growth rate have been calculated in the following groups of patients: 1 - untreated patients with pulmonary tuberculosis (PT), respiratory material; 2 - non-surgical treated PT patients, respiratory material; 3 - surgical treated PT patients (mainly with chronic and hy-perchronic process), respiratory material; 4 - patients like in 3^rd group, surgical material; 5 - bone and joint tuberculosis (BJT), surgical material. In addition, groups of sensitive and resistant strains have been examined, but there are no significant differences in growth rates. It has been obtained that the growth rate of strains isolated from the PT patients is higher than in BJT patients: it can be explained less favorable conditions for the pathogen vegetation in the BJT. In the case of a closed tuberculous lesion where the pathogen transmission to another host is impossible, then the selection of strains with the property to survive in the tissues of the osteoarticular system is impossible too, therefor it should be observed only an adaptation of the pathogen strain population to the individual host. The growth rate of isolates from untreated PT patients is higher than that of the treated ones. Comparison of the growth parameters of only MDR strains 1-5 groups to eliminate the influence of the sensitivity/resistance has resulted in the same conclusions. We suggest that the decrease in the growth rate of strains from the treated PT patients is in not only result of the treatment, but also is conditioned by adaptation of the pathogen to its external environment, which is the internal environment of the macroorganism. To confirm this assumption, the bacterial load of 1,083 diagnostic specimens grouped in a similar manner has been estimated, taking into account only MDR/XDR strains. In the group of treated patients the frequency of high bacterial load (CFU ≥ 100) reached 52.5-63.8% that shows the conserved fitness of bacteria in such patients. The mean values of the growth rate of the strain H37Rv non-adapted to the macroorganism (due to numerous passages on artificial media) are higher than in all groups of clinical strains. Thus, heterogeneity of phenotypic properties of M. tuberculosis clinical strains on the basis of growth rate has been obtained. The growth rate of M. tuberculosis clinical strains is depended on the tuberculosis localization (PT, BJT) and on the joint effect of patient treatment and pathogen adaptation to the host.