The Sick building syndrome (SBS) is a complex symptomology of individuals related to the adverse effects of indoor environment on health. Although almost any workplace can be affected it is most often associated with the office environment. The causes of SBS are not well understood, no single factor or agent has been identified. Some studies have indicated that SBS may be a result of multiple factors, including chemical, biological, physical, psychosocial, and occupational variables. One such variable, environmental tobacco smoke, has not been properly investigated as a contributing cause, and may be related to chemical sensitivity (CS). Some authors consider that victims of the SBS may be an example of chemical sensitivity and further that some CS patients become sensitive to electromagnetic fields (EMF) or electromagnetic radiations (EMR). The aim of this study is to investigate the effects of these potentially contributing factors to the sick building syndrome. 722 people in fifteen buildings with different ventilation systems were investigated via self-administrated questionnaires, in which data of SBS symptoms and ETS exposure and other information were collected. The results indicated that the combination of ETS exposure and working in air-conditioned office buildings contributed to the SBS symptoms in both uni-variate analysis, and multiple regression analysis, but neither of these variables individually has a significant effect on SBS. The contribution of environmental tobacco smoke is therefore considered to be small, but may be a contributing factor when taken together with other variables with air-conditioned buildings. In order to test the possible effects of electromagnetic fields on chemical sensitivity, 47 patients (19 sensitive to both electromagnetic fields and chemicals and 28 sensitive to chemicals only), and 34 controls were tested with sinusoidal uniform magnetic fields using Helmhotz coils in a single-blinded design study. The effects of exposure were tested by measurement of a number of physiological variables. Short time exposure to weak uniform sinusoidal magnetic fields at extremely low frequencies did not trigger more symptoms in chemical sensitivity patients than in controls. Significant changes in blood pressure and some parameters of pupil light reflexes were found in both CS patients and controls. Results indicate that ELF electromagnetic radiation may have an excitation effects on the sympathetic nervous system; however neither electrically sensitive nor chemically sensitive patients were more sensitive in these effects than controls. The contribution of tobacco smoke and ELF electromagnetic radiation to the cause of sick building symptoms needs further quantitative investigations.