ABSTRACTEarlier studies of Wistar rat respiratory epithelia exposed to low frequency noise (LFN) (≤500Hz, including infrasound) showed that LFN effects trauma on the respiratory tract. In rats gestated and born in LFN environments, trauma was still evident after spending 1 year in silence. This report studies Wistar rats gestated and born in a LFN environment and exposed to additional LFN. Wistar rats were gestated and born while exposed to LFN. After birth, the following groups were exposed to LFN for an additional 145hrs (Group A), 235hrs (Group B), 2213hrs (Group C), 2438hrs (Group D), 4399hrs (Group E), and 5304hrs (Group F). All animals were treated in accordance with 86/609/EC. Respiratory epithelial fragments were prepared for light and scanning/transmission electron microscopy. Group A brush cell (BC) microvilli tended to group together; in Group B they were clearly clustered together, and in Groups C-F they became fused. Rosetta structures (rings of secretory cells centered on a BC) were visible in Groups A-D and difficult to identify in Groups E,F. The amount of sheared cilia increased with exposure time, as did the images of cellular dedifferentiation. LFN exposure induces severe trauma on the respiratory epithelial cells in these rats.REV PORT PNEUMOL 2003; IX (6): 481-492