Long-term diabetes mellitus (DM) is characterized by widespread alterations of basal lamina (BL). The purpose of the present work was to verify whether the lung is also a target organ damaged in DM. Electron microscopy was performed on lung and kidney samples (autopsic material) from 6 diabetics and 6 control subjects studying the thickening of BL of different structures (alveolar epithelial BL, endothelial capillary BL, both fused BL, BL of the glomerular capillary endothelium and BL of the renal tubules). The results were as follows: (1) alveolar epithelial BL (mean +/- SD) = 121 +/- 11 nm in controls and 176 +/- 27 nm in diabetics (p < 0.01), (2) endothelial capillary BL = 164 +/- 14 nm in controls and 223 +/- 27 nm in diabetics (p < 0.001), (3) both BL fused = 222 +/- 23 nm in controls and 316 +/- 62 nm in diabetics (p < 0.01), (4) BL of the glomerular capillary endothelium = 374 +/- 44 nm in controls and 626 +/- 249 in diabetics (p < 0.05) and (5) BL of the renal tubules = 602 +/- 94 nm in controls and 1,083 +/- 376 nm in diabetics (p < 0. 05). All parts of the lung are equally affected by DM. The thickening of BL is of the same magnitude in lung and kidney. There is no relationship between the thickening of the lung BL and the known duration and type of DM.