Background: Benzalkonium chloride (BAC) is a quaternary ammonium compound (QAC) with a C8 to C18 chain length of alkyl groups. Since BAC exerts toxic effects on microorganisms, it has been used as an effective germicide and preservative, mostly in cosmetic industry and medicine. However, the toxic potential of BAC may be hazardous to humans, due to the common use of preparations containing BAC as a preservative. Material and Methods: To assess the possible toxic effects of BAC, two-stage experiments were performed on female Wistar rats. At first, LC50 after a single exposure to BAC aerosol was determined. Then, the animals were exposed to BAC aerosol at 30 mg/m3 for 6 h, and for 3 days (6 h/day). The controls were unexposed rats. Directly after BAC exposure and 18 h afterwards, BALF concentrations were measured of total protein, Clara cell protein, matrix metalloproteinase-9 (MMP-9), hyaluronic acid (HA), immunoglobulin E (IgE) and cytokines (TF-α, IL-6 and MIP-20), lactate dehydrogenase (LDH) and GSH-S-transferase (GST). Results: The LC50 value for exposed rats was ca. 53 mg BAC in m3 air for 4 h. All the rats survived single and repeated inhalation exposure to 30 mg/m3 BAC. After single and repeated exposure, lung weight, total protein, HA and LDH activity in BALF of exposed rats were higher than in controls while CC16 levels were decreased. A significantly higher BALF concentration of IL-6 and IgE was noted in animals exposed to single and repeated doses. BALF concentrations of MMP-9, TNF-α, and MIP-2 in exposed rats were similar to those in control animals. Conclusion: BAC may be classified to class I acute inhalation toxicity. It showed a strong inflammatory and irritant activity on the lungs after 6h inhalation and stimulated dynamic patterns of IL-6 and IgE production and protein infiltration from blood vessels to BALF. Continued exposure resulted in cellular destruction, a statistically significant increase in LDH activity and a continuous decrease in CC16 concentration in BALF.