Previous studies conducted in Catania hospitals have revealed a high burden of contamination in the air of operating rooms and have recommended measures to improve air quality. In this study we verified the effectiveness of the undertaken measures. Furthermore we evaluated the possibility of using microclimatic parameters as "markers" of operating room contamination. Changes made to ventilation systems and to waste gas scavenging systems in the monitored operating rooms were remarkably effective. Microclimatic conditions and degree of chemical contamination improved over time; nevertheless airflow velocity values were found to be insufficient and nitrous oxide values, in some cases, remained slightly elevated. A significant correlation was observed only between some nitrous oxide values and relative humidity. Monitoring important marker levels is useful for correctly evaluating operating room thermal, chemical and microbiological air quality.