AbstractAccording to an assessment protocol developed as a part of the INSULAtE project, indoor air quality measurements were conducted in three Finnish and Lithuanian multifamily buildings before and after energy retrofits. Additional cases from Estonia included one retrofitted and two non-retrofitted buildings. Measured gaseous pollutants included carbon dioxide (CO2), volatile organic compounds (VOCs), formaldehyde (CH2O), and nitrogen dioxide (NO2). Low CO2 concentrations in Finland could be attributed to common use of mechanical exhaust ventilation. WHO guidelines for CH2O were not exceeded in any of the measured apartments. No statistically significant changes were seen in VOC or NO2 after retrofits.