A tissue culture cell line CMT64 was established from a spontaneous alveolar lung carcinoma of a C57BL female mouse (Franks et al., 1976). Subcutaneous inoculation of these cells produced a local tumour and a small number of lung metastases. Four sublines CMT167, 170, 175 and 181 with increased metastatic ability were selected, as described in the accompanying paper (Layton & Franks, 1984). The tissue culture cells and the tumours produced by all the lines are well differentiated and produce laminated surfactant-like bodies as well as basal lamina, even in metastases. No ultrastructural differences were found that might correlate with metastatic behaviour in vivo. Metastases, after subcutaneous inoculation and tumour colonies after intravenous inoculation of all cell lines are only found in the lung, but after inoculation of cells into the arterial system via the left ventricle of the heart, extravascular tumour colonies were found in many organs.