Résumé : 153 strains, belonging to 5 different species of the genus Haemophilus isolated from pathological material of the respiratory tract, have been submitted to the action of inductive agents. Under their influence, all those strains, and consequently all the species examined, undergo morphological changes and give rise to spheroplasts. The present work demonstrates that this phenomenon not only belongs to Haemophilus influenzae but is probably a common characteristic of the genus Haemophilus.