The effects of the surfactant stimulating drug ambroxol were studied in rats given paraquat (PQ, 15 mg/kg, s.c.), intratracheal cobalt chloride (CoCl2, 2.5 or 1.25 mg Co/kg) or exposed for 2 days to oxygen (greater than 95% O2). Ambroxol (50 mg/kg, i.p., twice daily) was given as a pretreatment for 4 days, or up to 7 days following pneumotoxic administration. Besides body weight evolution and lethality, various pulmonary indices were measured 2 days (O2) or 3 days (PQ and CoCl2) and 7 days after pneumotoxic treatment: wet and dry lung weight, total cell count, distribution of inflammatory cells and lactate dehydrogenase in bronchoalveolar lavage fluid, and histological damage assessed by a semiquantitative injury score. Neither form of ambroxol treatment prevented the toxicity of any of the pneumotoxic agents. The use of a combination of different indices of lung damage showed that different pneumotoxic agents may cause quite distinctive patterns of injury.