The construction and performance of an instrument which is portable, self-powered, intrinsically safe in mine atmospheres and designed to be left to operate unattended during a working shift are described.Following its aerodynamic selection by passage through a `horizontal elutriator', the `respirable' dust is collected on a glass fibre paper filter through which air is drawn by a reciprocating diaphragm pump driven by a governed 6 v motor. Air flow rate (2.5 l. min^-1) is largely independent of build-up in filter resistance, and the glass fibre paper is little affected by ambient moisture. Simple estimation of coal/non-coal content of the sample is given by incineration of the dust on the filter.