Ultrastructural and functional changes induced by mineral dusts in alveolar macrophages were studied in-vitro. Suspensions of alveolar macrophages prepared from guinea-pigs were incubated with quartz (14808607) or titanium-dioxide (13463677) dusts for 2 hours. The suspensions were examined for organelle damage by transmission electron microscopy (TEM). Alveolar macrophage suspensions were incubated with quartz, asbestos (1332214), graphite (7782425), titanium-dioxide, antimony (7440360), or beryllium (7440417) dusts. Alveolar macrophage suspensions were incubated with quartz. Vitamin- E, superoxide-dismutase (SOD), P240, or piperaquine was added to assess their ability to protect against quartz induced cell membrane damage. Quartz disrupted cellular lysosomes, increased mitochondrial pyknosis, caused swollen nuclei, nuclear vacuolation, and disrupted the nuclear envelope. Few pseudopodia were visible. Some necrosis was observed. Titanium-dioxide caused less severe changes, expanded cellular volume and increased numbers of pseudopodia being the major changes seen. Quartz disrupted the cell membrane. Frequent vacuolation and loss of pseudopodia and microvilli from the membrane were observed. Short asbestos fibers were absorbed and phagocytized in-situ by the macrophages. Long asbestos fibers were phagocytized in a sleeve like fashion. Asbestos fiber phagocytosis was accompanied by increasing cellular death. Antimony dust caused membrane ruffling. Beryllium caused straw hat/like changes in the membrane structure. Graphite caused no obvious membrane changes. Titanium-dioxide particles were phagocytized in-situ with little changes in membrane structure being observed. Vitamin-E, SOD, P204, and piperaquine protected against quartz induced membrane damage. Quartz, asbestos, graphite, and titanium-dioxide inhibited protein synthesis by 32.1, 43.4, 8.8, and 25.3%, respectively. The authors conclude that quartz is the most cytotoxic to alveolar macrophages. Asbestos has the most suppressive effect on macrophage protein synthesis.