AbstractIndoor air bacteria and fingal spore levels were studied in 71 non‐complaint homes. lk data were analyzed according to the season and the higher limit of the range within which 95% of the cases fall was computed. On the basis of the data the following highest normal levels are proposed for winter: for bacteria 5000 cfulm3and for fingal spores 500 cfulm3. The recommended levels apply in a subarctic climate for urban and suburban homes when the measurements are made using the same method as in this study. We recommend that if abnormal indoor sources are suspected, indoor samples should be taken in winter when the ground is frozen and covered with snow. At that time, the background levels are at their lowest and the abnormal indoor sources are most easily detected. lk recommended levels should not be used as an indicator of a health risk, but as an indication of abnormal indoor sources or insufficient ventilatio