The purpose of this study was to investigate whether photocatalytic TiO(2) nanoparticles have adjuvant effect, when administered in combination with ovalbumin (OVA) in mice. Mice were immunized via intraperitoneal injections of OVA, OVA + TiO(2) or OVA + Al(OH)(3) and challenged with aerosols of OVA. At the end of the study, serum was analysed for content of OVA-specific IgE, IgG1 and IgG2a antibodies, and the bronchoalveolar lavage fluid (BALF) was analysed for content of inflammatory cells and levels of interleukin (IL)-4, IL-5, IL-10 and interferon-gamma. The TiO(2) particles promoted a Th2 dominant immune response with high levels of OVA-specific IgE and IgG1 in serum and influx of eosinophils, neutrophils and lymphocytes in BALF. The TiO(2) particles induced a significantly higher level of OVA-specific IgE than the standard adjuvant Al(OH)(3). However, the two substances were comparable regarding the level of eosinophilic inflammation and interleukins present in BALF.