We studied leukocyte chemotaxis triggered by a local injection of mycobacteria (Mycobacterium avium and M. smegmatis) in BALB/c and C57BL/6 mice. Our experimental model consisted of the induction of a subcutaneous air pouch in the dorsal area of mice and inoculation 6 days later of 108 CFU of mycobacteria. Inflammatory exudates were harvested from the air pouch cavities 15, 30, and 45 min after the injection of the inocula. Injection of the microorganisms resulted in the migration of an elevated number of eosinophilic granulocytes into the inflammatory cavities. At 30 min after the inoculation of the mycobacteria, the air pouches contained between (3.9 + 0.3) x 105 (M. avium) and (3.3 ± 0.3) x 105 (M. smegmatis) eosinophils, corresponding to more than one-third (41.4 to 38.3%) of the leukocytes present in the inflammatory cavities. Less than one-half of the eosinophils were attracted to the air pouches when the same number of heat-killed mycobacteria were inoculated [(1.3 + 0.2) x 105 cells for M. avium and (1.5 ± 0.2) x 105 cells for M. smegmatis]. Injection of gram-negative bacteria (Escherichia coli), of latex beads, or of casein resulted in the