3T3-L1 cells were induced to differentiate as described in Methods. Cells were assessed for degree of adipocyte differentiation after ten days of differentiation while exposed to indoor house dust extracts diluted to approximately 100 μg/mL concentration. (A) The proportion of samples exhibiting significant adipogenic activity relative to the differentiated vehicle control for triglyceride accumulation only, pre-adipocyte proliferation only, or a combination of both triglyceride accumulation and pre-adipocyte proliferation. Reporter gene assays were used to measure activation of the peroxisome proliferator activated receptor gamma (PPARγ) and inhibition of the thyroid receptor beta (TRβ) as described in Methods. A) The proportion of dust extracts exhibiting significant activation of PPARγ, inhibition of TRβ, both, or neither PPARγ agonism nor TRβ antagonism.