Exposure to endotoxin has been associated with increased respiratory symptoms and decrements in lung function in occupational settings but little is known about health effects of domestic exposure in adults. We describe the association of respiratory disease, IgE sensitisation, bronchial reactivity and lung function with mattress endotoxin levels in adults and determine whether these associations are modified by polymorphisms in CD14.Endotoxin levels in mattress dust from a population based sample of 972 adults were measured. Associations were examined using generalized linear mixed models, adjusting for individual and household confounders. Effect modification of these associations by CD14/-260 (rs2569190) was assessed.Mattress endotoxin levels varied from 0.1 to 402.6 EU·mg(-1). Although there was no overall association of lung function with endotoxin exposure, there was evidence that the association of FEV1 and FVC with endotoxin was modified by CD14/-260 genotype (p for interaction 0.005 and 0.013 respectively). There was no evidence that symptoms, IgE sensitisation or bronchial reactivity was associated with mattress endotoxin levels.In this large epidemiological study of adults there was no evidence that mattress endotoxin level was associated with respiratory symptoms or IgE sensitisation but the association of lung function with endotoxin levels may be modified by CD14-genotype.