This repetitive pattern was surprising in view of the large differences between the buildings in terms of office accommodation (some were open plan, others had small offices), humidification system, and amount of air recirculated. The prevalences of the symptoms affecting the upper respiratory tract and mucous membranes were high, especially in the humidified buildings, when compared with those in the naturally ventilated buildings. Indeed, in one building (building 8) over half the employees questioned were affected by dryness of the mucous membranes. Part of the high prevalence of symptoms in building 5 may have been explained by dissatisfaction with a new working environment as the workers had all recently been moved to this air conditioned office from a naturally ventilated one.