Rationale. Exposure to particulate matter is associated with risk of cardiovascular events, possibly through endothelial dysfunction and indoor air may be most important. Objective. We investigated effects of controlled exposure to indoor air particles on microvascular function as the primary endpoint and biomarkers of inflammation and oxidative stress as secondary endpoints in a healthy elderly population. Methods. Twenty-one non-smoking couples participated in a randomized, double-blind, cross-over study with two consecutive 48-h exposures to either particle filtered or non-filtered air (2533-4058 and 7718-12988 particles per cm³, respectively) in their homes. Measurements and results. Microvascular function was assessed non-invasively by measuring digital peripheral artery tone following arm ischemia. Secondary endpoints included hemoglobin, red blood cells, platelet count, coagulation factors, P-selectin, plasma amyloid A, C-reactive protein, fibrinogen, interleukin-6, tumor necrosis factor alpha, protein oxidation measured as 2-aminoadipic semialdehyde in plasma, urinary 8-iso-prostaglandin F₂ and blood pressure. Indoor air filtration significantly improved microvascular function by 8.1% (95% confidence interval: 0.4-16.3%) and the particulate matter (diameter<2.5µm) mass of the indoor particles was more important than the total number concentration (10-700 nm) for these effects. Microvascular function was significantly associated with personal exposure to iron, potassium, copper, zinc, arsenic and lead in the fine fraction. After Bonferroni correction none of the secondary biomarkers, changed significantly. Conclusion. Reduction of particle exposure by filtration of recirculated indoor air for only 48-hours improved microvascular function in healthy elderly citizens suggesting that this may be a feasible way of reducing the risk of cardiovascular disease.