Experimental studies of human maxillary sinus gas exchange show that there is a balance between inflow of air through the maxillary ostium and local consumption as long as the functional size of the ostium is at least 5 mm2. Maxillary sinus mucosal blood flow is 30-40 ml/100 g tissue per minute, as measured in plethysmographic studies. This blood flow can bind and transport only half of the absorbed oxygen, the rest is consumed. Experimental histo- and biochemical studies of sinusitis show anaerobic mucosal metabolism with shortage of energy supply due to inadequate oxygen supply. There is no decrease in oxidative enzyme capacity of the mucosal epithelium. Analysis of organic acids in purulent secretion indicates that the high lactate and CO2 concentration found is mainly the result of leucocyte glycolysis with local lactic acidosis. Both ostial occlusion and the initiation of bacterial growth in serous sinusitis may be secondary to an initial inflammatory response, resulting in local tissue pathology and swelling of the ostiomeatal complex, as well as creating the appropriate redox potential for further bacterial growth in the secretions.