BACKGROUND:Many outdoor fungal spores are ubiquitous, respirable and possibly allergenic. They may contribute to asthma symptoms; however, little is known about their effects on respiratory function. OBJECTIVE:To investigate if outdoor fungal spore levels were associated with lung function or airway inflammation, and whether fungal sensitization or current asthma modified any associations. METHODS:Cross-sectional associations between same day (Lag0) and cumulative 3-day lagged (Lag0-3) counts of 12 outdoor fungal spore taxa and pre-bronchodilator spirometry (FEV1, FVC, FEF25%-75%), bronchodilator response (BDR) and airway inflammation (fractional exhaled nitric oxide (FeNO) and exhaled breath condensate (EBC) nitrogen oxides (NOx) and pH were investigated in 936 Melbourne Atopy Cohort Study participants during September 2009 to December 2011. Generalized linear models were used to quantify associations with lung function, FeNO and EBC pH; generalized estimating equations for BDR; and ordinal logistic regression for EBC NOx. Models were adjusted for age, sex, height, temperature, relative humidity, grass pollen and sample storage time. Potential effect modification by fungal sensitization and current asthma were examined using interaction terms. RESULTS:Mixed associations were found. Higher levels of Ustilago/smuts were associated with lower lung function at Lag0 (FEV1: 21ml [95%CI -36, -7]; FEF25%-75%: 39ml [-65, -13]) and Lag0-3 (FEV1: 9ml [-14, -4]; FEF25%-75% -18ml [-27, -9]). Positive BDR was associated with Ustilago/smuts (Lag0 OR = 1.1 [1.04, 1.2]; Lag0-3 OR = 1.04 [1.02, 1.07]), Alternaria (Lag0 OR = 1.3 [1.0, 1.6]) and Drechslera (Lag0 OR = 1.1 [1.03, 1.2]). Higher EBC NOx was associated with Cladosporium (Lag0-3 OR = 1.1 [1.0, 1.2]), Alternaria (Lag0-3 OR = 1.1 [1.0, 1.3]). No associations were found with higher FeNO. In those with fungal sensitization, Ustilago/smuts and Drechslera were associated with lower FEV1 and FVC; Cladosporium was associated with increased FEV1, FVC and FEF25%-75% but also with higher FeNO and lower EBC pH. In those with current asthma, Alternaria, Ustilago/smuts and Drechslera were associated with lower FEV1, FVC, FEF25-75% and EBC pH. CONCLUSION:Exposure to outdoor fungal spores may be associated with lower lung function and increased airway inflammation, particularly in those with fungal sensitization and/or current asthma.