The results of industrial hygiene investigations of two office buildings in which occupant complaints indicative of tight building syndrome and hypersensitivity pneumonitis like illnesses were reported were summarized. An office complex had a long history of problems associated with proliferation of molds resulting from floods that were due to roof leaks and a relative humidity frequently exceeding 70% during the summer. Frequent complaints of dyspnea, persistent cough, fatigue, and eye, nose, and throat irritation were reported by the occupants, especially those who worked on the lower floors. Inspection of the heating, ventilation, and air conditioning system and measurements of air flow indicated that the office complex was inadequately ventilated. A microbial contamination survey found that stagnant water and slime in drain pans for the major air handling units (AHUs) and peripheral fan coil units contained bacteria concentrations of 1x10(7) per milliliter. Dust from one small AHU filter contained 3x10(7) viable fungi per gram. Airborne fungal concentrations ranging up to 94000+ colony forming units per cubic meter (CFU/m3) were measured in some offices at a time when fungal concentrations in the outside air were 50 to 500CFU/m3. An 18 story building experienced a massive flood on the second, first, and mezzanine floors due to a break in the plumbing lines serving a heat pump above the second floor ceiling. Despite vacuuming and treating flooded carpets with germicidal chemicals, persistent employee complaints of headache, eye and throat irritation, and chills and flu like symptoms occurred. The building air handling system supplied inadequate amounts of outside air. Airborne fungal concentrations in areas that had been flooded averaged 10200CFU/m3. Airborne fungal concentrations in nonflooded areas were around 3000CFU/m3. Suggested remedial actions for the two buildings were presented. These include preventing moisture incursion into occupied areas, initiating a preventive maintenance program of the air handling systems of the office complex, replacing carpet that has been flooded, and upgrading the air handling systems. The author concludes that a viable microorganism concentration of 1x10(3)CFU/m3 in an office environment may be a useful index of excessive microbial exposure.