Groups of 20 female CBA mice were injected subcutaneously in two sites with suspensions of crocidolite, amosite or chrysotile asbestos. Each injection consisted of 10 mg fibre suspended in 0.4 ml saline and each animal received 3 injections into each flank at sites well distant from the thorax. For comparison, two groups were similarly treated with crocidolite and amosite from which natural and contaminant oils had been removed by solvent extraction. The most remarkable feature of the results were, first, the apparently specific transport of asbestos fibres of all three types to the submesothelial tissues of the thorax and abdomen; and secondly, the development of extensive inflammatory and proliferative changes in these regions culminating, in 10 instances, in the formation of mesotheliomata. Six animals developed sarcomas at the injection site but, in most mice, there was little cellular response to asbestos in the subcutaneous tissues in contrast to the vigorous reactions seen in serosal membranes. All three types of asbestos induced both injection-site tumours and distant mesothelial changes and the removal of oils from amosite and crocidolite did not abolish—though it may have reduced—these manifestations of carcinogenic activity.