Transmission electron microscope examination of 47 autopsy lung samples from Quebec miners and millers showed that tremolite was present in approximately similar quantities to chrysotile (with crocidolite and amosite in much smaller amounts), although the quantity of tremolite compared with chrysotile in the ore worked was extremely small. These findings suggest that chrysotile was probably removed from the lungs while tremolite was retained. In spite of this removal, however, it seems that the chrysotile content of lung tissue can serve as an indicator of past exposure. The effect of the interval between exposure and death will be examined later. The design of the study does not permit evaluation of the contribution of tremolite to pulmonary fibrosis in Quebec miners and millers.