OBJECTIVES: The objective of this study was to determine whether verified increased nasal mucosal reactivity among teachers, who had been working in a school with severe moisture problems, still persisted 6 years after remedial measures had been taken. The increased nasal mucosal reactivity, measured as the mucosal swelling reaction upon histamine provocation, had earlier been shown both 1 and 3 years after the renovation. METHODS: Twenty-four teachers in the target school and sixteen teachers in the control school, who participated in all the investigations (1995, 1997 and 2000), answered a standardized questionnaire and underwent a nasal histamine provocation test. In addition to the registration of mucosal swelling, the microcircular reaction to histamine provocation was measured with laser-Doppler flowmetry. RESULTS: The nasal histamine reactivity among the teachers, measured as the mucosal swelling reaction, was no longer increased. However, the laser-Doppler flowmetry showed that the teachers in the target school had significantly divergent microcircular perfusion (P=0.0022) and a concentration of moving blood cells (P=0.0009) in the histamine provocation when compared with the teachers in the control school; this finding indicates more-pronounced plasma leakage and edema from the nasal mucosa. CONCLUSIONS: Restored nasal histamine reactivity, measured as mucosal swelling reaction, was observed among the teachers 6 years after an obviously successful renovation of the school environment. However, changes in microcirculation indicate a remaining effect on the nasal mucosa.