Used ventilation air filters have been shown to reduce indoor environmental quality and worker performance and increase symptoms, with effects stronger after reaction of filters with ozone. We analyzed data from the U.S. EPA Building Assessment Survey and Evaluation (BASE) study to determine if ozone and specific filter media have interactive effects on building-related symptoms (BRS). We analyzed a subset of 34 buildings from the BASE study of 100 U.S. office buildings to determine the separate and joint associations of filter medium (polyester/synthetic (PS) or fiberglass (FG)) and outdoor ozone concentration (above/below the median, 67.6 mg/m3) with BRS. Using logistic regression models and general estimating equations, we estimated odds ratios (ORs) and 95% confidence intervals for the association of filter medium, ozone, and filter medium*ozone with BRS. Relative to FG+low ozone, PS alone or high ozone alone each were significantly (p<0.05) associated only with fatigue/difficulty concentrating (ORs = 1.93, 1.54, respectively). However, joint exposure to both PS+high ozone, relative to FG+low ozone, had significant associations with lower and upper respiratory, cough, eye, fatigue, and headache BRS (ORs ranged from 2.26-5.90). Joint ORs for PS+high ozone for lower and upper respiratory and headache BRS were much greater than multiplicative, with interaction p-values < 0.10. Attributable risk proportion (ARP) estimates indicate that removing both risk factors might, given certain assumptions, reduce BRS by 26%-62%. These findings suggest possible adverse health consequences from chemical interactions between outdoor ozone and PS filters in buildings. Results need confirmation before recommending changes in building operation. However, if additional research confirms causality, ARP estimates indicate that appropriate filter selection may substantially reduce BRS in buildings, especially in high ozone areas.