Moisture damage and microbial growth in buildings are associated with adverse health effects and morbidity although no linear association with viable microbes and health effects has been found. Mycotoxins and bacterial toxins have been suggested to be causing symptoms, but concentrations of toxins in indoor air are often extremely low or not detected. Clear recommendations and also consensus about of toxicity measurements are lacking. Our pilot study shows that in buildings where potentially toxin-producing microbes can be identified, some samples are toxic when measured with a new E. coli lux –test. The respondents report more symptoms than the reference group in another building with neither microbes nor toxicity can be found.