The authors have performed 58435 microscopic examinations, of which 3813 were positive, and found 209 (5,48%) cases of non-cultivable Koch bacilli. The major bacteriological, clinico-evolutive and therapeutical aspects are examined. Most of the cases showing a syndrome of positive homogenate with a negative culture were rather recent ones (an evolution of less than 2 years in 73,68% of the total) and the highest frequency was found in those in which the treatment was in its first year. No direct relationship could be demonstrated between the number of germs (the Gaffky scale) and the frequency of the syndrome. The factors influencing the occurrence and the development of the syndrome are: the structure of the lesions, the method of bacteriologic examination, the therapy applied, and a certain immunologic reactivity. According to the authors the significance of this syndrome is positive in most of the cases, indicating a regression that has not been completed. The most reasonable attitude is a differentiated one, depending on each case, integrating the data obtained by the bacteriological examination in the therapeutic and evolutive clinico-radiologic context.