Abstract Preliminary results are reported from an International study on the mineral content of respirable coalmine dusts, the toxicity of these dusts as recorded by short-term in vitro and in vivo tests and their relationship to epidemiological data on levels of pneumoconiosis in the collieries concerned. The results from the mineralogical analyses show extremely good correlation between the different laboratories involved. In general, the correlations between the in vitro biological results are poor, although in most cases there was agreement on which were the most toxic dusts. At present, no information is available from the in vivo studies or from epidemiological comparisons.