The Institute of Hygiene was requested to determine causes and scope of health complaints made by the employees of Haldensleben district administration after sound absorbing mineral fibre boards had been installed as suspended ceilings. The boards were coated with a lean water-carried paint; however, the edges, which were partially frayed, were not coated. The air inside the rooms was measured on all four storeys of the building, followed by scanning electron microscopy in compliance with VDI Code 3492. In addition, measurements showed fibres with diameters of > 3 microns which are not subject to the regulations for carcinogenic substances, but, in contrast to the thinner fibres, they may cause irritations of skin and mucosa. The employees were questioned about their health problems. At the beginning of 1994, a total of 79 of the 133 employees complained about itching, reddening and burning of their eyes as well as irritations of the upper respiratory tract. More than 50% had consulted a doctor. Late in 1994, another questionnaire survey was completed. The fibre content of the office air was determined to vary from 1000 to 3500 fibres/m3 and, in addition, 100-200 fibres with diameters of > 3 microns. Our investigations showed that there is an interrelationship between the degree of dust accumulation in the offices and health complaints. Independently of the current discussion of the cancer causing potential of thin man-made mineral fibres, the very long and thick mineral fibres (> 3 microns in diameter) are of topical importance to health.