Pigmented Neisseria species (Neisseria perflava, flava, subflava, sicca) are constant inhabitants of patients with infectious asthma. 2. Of all the diverse bronchial microflora of patients with infectious-allergic bronchial asthma, the pigmented Neisseria species (Neisseria perflava, flava, subflava, sicca), Staphylococci (Staphylococcus aureus, epidermidis), Klebsiella (Klebsiella pneumoniae) are active sensitizers of the human broncho-pulmonary tract. 3. Neisseria strains, possessing similar antigenic determinants to human lung tissues, possess the highest allergenic activity. This raises the question of a new criterion for evaluating the allergenicity of cultures according to their antigenic characteristics. 4. In patients with infectious asthma allergy might develop to some of the structures of microbial cells, in which antigenic determinants, similar to human lung tissues are localized.