Persistent health problems have been observed since 2006 among staff at a cancer research center and staff at other laboratories located on the same floor of the Institute of Biology at the Nantes University Hospital. A retrospective survey was conducted using a self-administered questionnaire among the affected staff. Among the 183 respondents, 71% reported experiencing irritative symptoms (ENT, ocular, or cutaneous), general symptoms, digestive symptoms, or respiratory symptoms at their workplace in 2006 or 2007. The prevalence of symptoms increased from 22% in the first half of 2006 to 52% after October 2007. Two peaks in reports were observed in January 2007 (following the closure of cell culture rooms) and in October 2007 (following a spike in odors). The frequency of symptoms was significantly higher among women, engineers or technicians, individuals using disinfectants, and those with a negative perception of humidity, temperature, or air exchange at their workstations. Outside an area served by one of the five air handling units, the frequency of symptoms was consistent among staff working in the rest of the premises. Environmental studies confirmed poor ventilation, temperature, and humidity conditions without excessive concentrations of volatile organic compounds. According to the opinion of consulted toxicology experts, a toxic hypothesis appears unlikely. These events are described in the literature as sick building syndrome. (R.A.)