Mollicute-Like Organisms (MLO) are cell-wall deficient intracellular bacterial pathogens. As MLO are non-cultivable, detection is based on finding typical Mollicute bodies within the host cell using a transmission electron microscope. Extracellular Mollicutes cause disease by a variety of mechanisms. MLO cause disease by similar mechanisms, and in addition directly alter the host cell nucleus, replace the cytoplasm, and destroy the organelles. MLO parasitization of plant cells causes a well studied chronic vascular disease reversible by tetracycline antibiotics. Recently similar MLO were reported to cause human chronic ocular vasculitis. As it parasitizes, lyses, and destroys leucocytes, it has been termed Leucocytoclastic MLO. Inoculation of this MLO into mouse eyelids produced delayed onset chronic ocular and lethal cardiac vasculitis. All lesions demonstrated tissue lysis with leucocytic infiltrates and MLO parasitized leucocytes. MLO-caused human and mouse disease responds to Rifampin. This report describes the 40 interstitial lung disease lesions in 21 of 100 of those MLO inoculated mice vs 0 in 200 controls (P less than 0.05) and 27 pleuritis lesions in 17 mice vs 0 control mice (P less than 0.05). The lung and pleural disease were associated in 13 lesions and unassociated in 41 lesions. MLO parasitized leucocytes were found in both the lung and pleural lesions from six of six MLO inoculated mice versus none of six controls. As most human interstitial lung and pleural diseases are idiopathic and closely resemble this mouse disease, they may be induced by MLO and treatable by Rifampin.