In the present work, ARMS2 gene- and protein expression were identified in human induced pluripotent stem cell-derived microglia (iPS-derived microglia) and human monocytes by PCR and laser scanning microscopy, whereas no expression was detected in murine macrophage RAW264.7. For the first time, endogenous ARMS2 was localized in the cytoplasm of human blood-derived monocytes as determined by fluorescence microscopy and three different ARMS2 antibodies. ARMS2 is weakly expressed in monocytes, but synthesis increased upon oxidative stress, indicating that ARMS2 is involved in the response to oxidative conditions. To confirm its expression, ARMS2 was pulled down from THP-1 cell lysate by immunoprecipitation using a newly generated ARMS2 monoclonal antibody and ARMS2 peptides were identified by mass spectrometry. AMD patients homozygous for the risk variant (rs10490924) showed no ARMS2 protein in their blood-derived monocytes, thus supporting the instability by the indel variation.