The quartz content of respirable airborne dost is determined from samples collected on 13-mm silver membrane filters which are analyzed by x-ray diffraction and transmittance measurements. These determinations (including the weight of the deposits and volume of air sampled) lead to the evaluation of the silicosis hazard at the sampling site. Dust deposits having a wide range of weight and composition may be analyzed with a precision of better than 3%; in addition, with laboratory preparation of filter deposits, the x-ray analytical technique may be applied to crushed parent material, lung ash or other samples. The theoretical considerations of the x-ray (diffraction and transmittance) analytical technique are presented, along with reasons for recommending this methodology as a guide-line procedure for assessing the health hazard of almost any siliceous-type dust.