Because the diagnosis of extrinsic allergic bronchiolo-alveolitis is usually on a clinical and serologic basis, recent histopathologic descriptions of the syndrome are rare. As the etiology may vary in different countries, so perhaps may the histopathology? Clinical and serological examination was combined with histopathology of open lung biopsy from 14 northern Finnish patients. All of them, after exposure to mouldy dust, had a typical clinical syndrome with cough and/or dyspnoea, some radiographic changes, and a reduced VC and/or DCO. Precipitating antibodies were demonstrated in 11 patients. Histopathologically, oedema, macrophages and granulomas were found in all patients, as were lymphocytic and plasmocytic infiltrates. Inflammatory changes were alveolar, interstitial and bronchiolar, including bronchiolar granulomas in all but one case. None of the patients had severe fibrosis or emphysema. There were no examples of clear-cut acute or chronic stages as described in previous studies. Instead, most of our specimens represented an "intermediate" stage, indicating differences in exposure or susceptibility of the population compared with other countries.