Macrophages have a direct role in the inflammatory response to cadmium exposure. Cadmium is not only an important air pollutant, but is also one component of cigarette smoke. To study the effects of soluble cadmium on macrophages, two model systems were chosen:rabbit alveolar macrophages (RAMs) obtained by pulmonary lavage and peritoneal macrophages elicited by intraperitoneal injections of 10(7) viable M. bovis, bacillus Calmette Guérin (BCG MACs). Macrophages were maintained in standard tissue culture medium from 4 to 30 hours with concentrations of cadmium chloride (CdCl2) ranging from 0 to 1.0 mM. Attached macrophages and RAMs in suspension were studied by conventional transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive x-ray microanalysis (EDX). In addition to routine techniques for TEM and SEM, preparatory procedures included snap freezing in liquid propane, and either cryoultramicrotomy or freeze-substitution with 1% osmium tetroxide in acetone. By TEM many macrophages exhibited laminated nuclear inclusions at doses as low as 0.05 mM CdCl2) (at 20 hrs) and as early as 4 hrs (at 1.0 mM CdCl2). Sections of cells fixed by freezing exhibited the same nuclear inclusions as well as mitochondrial densities that were not visible with any other preparative technique. Cadmium was demonstrated in the nuclear inclusions and mitochondrial densities by EDX in snap frozen cells. Lesser amounts of cadmium were also detected diffusely in treated cell cytoplasm and nuclei. Cadmium was only detected by EDX in cells fixed by freezing. These studies document the localization of Cd in nuclear inclusions and mitochondria providing morphological support for the biochemical findings of other laboratories. In addition, the value of fixation by freezing over conventional chemical fixation is illustrated.