According to literature, siderophages are a characteristic histological finding in the lung of deceased drug addicts (IVDA). It was the aim of our study to evaluate their pathognomonic significance. The lungs of 591 drug deaths in Hamburg were examined histologically for siderophages in two series, with different 'Berlinerblau' (Prussian blue) staining methods. The first series (investigation period 1980-1990) showed iron-containing macrophages in 36 of 420 drug deaths (8.6%) compared with a control-group (healthy young persons dying from unnatural causes of death) in which only one was positive (2%). In a second series, using a more sensitive staining method, 80 of 171 drug deaths (47%) in the year 1991 showed siderophages, whilst in a control-group, 17 of 35 cases (49%) were positive. According to our findings the pathognomonic value of siderophages in the lung of IVDA is doubtful. There is a need for further histochemical and ultrastructural investigations concerning the morphology and etiology of pulmonary macrophages in IVDA.