It is well known that in many cases the responsibility for the formation of the sick-building syndrome lies with the inappropriate envelope design, the misuse of the building by the inhabitants and the combination of indoor-outdoor pollution sources. In the case of Athens Air Traffic Control Tower (ATCT), sick syndrome episodes were reported by the employees. In the present study, recently obtained indoor air quality measurements, during selected meteorological conditions, taken in the ATCT, are presented and discussed. These include concentrations of volatile organic compounds (VOCs), which in many cases were thought responsible for the poor indoor environment. The measurements cover the indoor and outdoor environment of selected building regions, the ventilation systems and the plenum under the floor. The data indicates that there are certain places in the building where the VOCs concentrations were well above outdoor levels, while in others the concentrations were lower. Further analysis of the results showed that the central ventilation system is not sufficient for the building needs and that in some areas, either due to cleaning negligence or to the construction material used, VOCs pollution sources have developed. In order to eliminate these problems and to improve the indoor environment certain actions were taken, Following these interventions a second set of measurements were collected, inside and outside the ATCT building, which indicated a substantial improvement of the indoor air quality. (C) 2003 Elsevier B.V. All rights reserved.