Potential risk associated with new nanomaterial exposure needs to be assessed. This in vivo study investigated pulmonary effects of engineered cadmium-containing silica nanoparticles Cd/SiNPs (1 mg/rat), silica SiNPs (600 μg/rat) and CdCl₂ (400 μg/rat) 1, 7 and 30 days after intratracheal instillation. Comprehensive histopathological and immunocytochemical characterization of lung damage in terms of apoptosis, cell proliferation, inflammation, fibrosis and metabolism were obtained. After exposure to all treatments, lung parenchyma showed injury patterns characterized by collapsed alveoli, inflammation, granuloma formation, thickened alveolar septa and bronchiolar epithelium exfoliation. Type II pneumocytes, containing scarcely surfactant-lamellated bodies, were also observed. Apoptotic phenomena enhanced as following, Cd/SiNPs>CdCl₂> SiNPs. In parallel with these findings, a significant increase of PCNA-immunoreactive cells was detected together with high mitotic activity. Cellular localization and distribution of IL-6, IP-10 and TGF-β1 revealed an increased expression of these cytokines as evidence of an enhanced cellular inflammatory response. CYP450-immunoreactivity was also enhanced, at bronchiolar (e.g. Clara cells) and alveolar (e.g. macrophages) level after both Cd/SiNPs and CdCl₂. These overall effects were observed acutely and lasted until the 30th day, with Cd/SiNPs producing the most marked effects. Collagen-immunolabelling changed particularly 7 and 30 days after Cd/SiNPs, when a strong stromal fibrogenic reaction occurred. The present findings suggest that Cd/SiNPs produce significantly greater pulmonary alterations than either SiNPs or CdCl₂ under the present experimental conditions.