A short-term toxicological test has been developed using a calorimetric method. The metabolic activity, observed as the heat exchange rate, was monitored from alveolar rabbit macrophages in monolayers exposed to different metal and non-metal particles. Calorimetric activity indices and viability indices were introduced, from which toxic effects could be assessed. Manganese dioxide particles were found to be cytotoxic. In contrast, titanium dioxide particles seemed to be harmless. The results were in accordance with the cell survival found by use of a fluorescein ester staining method and measured by an image analyzer. Toxic effects from quartz in the form of increased metabolic activity of exposed cells could be detected by the calorimeter in contradiction to the use of the image analyzer. This latter result supports the hypothesis that silica particles cause chronic modification of the macrophage function and that this change in the alveolar macrophage function may be the first of a series of processes leading to pulmonary fibrosis.