SummaryA sensitivity study of 288 M.tuberculosis strains, isolated in the area of Brussels during the past year (May 1969 to May 1970), to specific antibiotics, lead to the following considerations :1) a large number of strains remained sensitive to streptomycin (85 %), to PAS (95 %), to INH (84 %) as well as to all the tuberculostatic drugs applied (75 %).2) in most cases the new patients had been sheltering sensitive strains; almost all the resistant strains originated, when the previous case history could be established, from well-known tuberculous patients who had already been submitted to chemotherapy.3) among the 29 multiple resistant strains, 3 (10 %) were resistant to rifam-picin; on the contrary, no resistance has been detected to ethambutol.4) in newly detected patients, the choice of an anti-tuberculous therapy, previously to the results of the antibiogram, presently remains largely open and the medication has to be established in function of clinical criteria as well as criteria concerning therapeutical efficacy.