A technique for collecting single raindrops for the observation of particulates by transmission electron microscopy is described. Measurement of particulate concentrations in raindrops during the course of rainstorms over central New Mexico has shown that the particulate concentrations increase from the onset of rain, reaching a maximum concentration which then declines exponentially with elapsed time. The particulates were observed to vary in size from less than 0.01 to 3μ, with a mean particle size of 0.1μ. Essentially all of the particulates were observed to be crystalline or polycrystalline aggregates composed mainly of micas, kaolinites, and other layer silicates. The particulate morphologies exhibited a pre-ponderance of platelike structure or aggregates possessing a large surface-to-volume ratio. Asbestiform fibers were not abundant in the distribution of seavenged particulates, and the dearth of observations of such fibers in raindrops for this particular area supports earlier conclusions that very high fiber concentrations in potable water of the region have their origin in geologic or hydrologic mechanisms.