Chronic exposure of hamsters to chrysotile asbestos resulted in severe asbestosis in all animals and in increased mortality; concomitant exposure to cigarette smoke did not affect type or severity of asbestotic lesions. Chronic exposure to asbestos-cement dust increased the number of macrophages and ferruginous bodies. Exposure to talc baby powder caused no significant changes. Deposition of talc particles in the lungs was demonstrated by X-ray fluorescence and X-ray diffraction and by a study with neutron-activated talc. No malignant tumours were observed in any of these studies.