Microglial cell function receives increasing interest. To date, the majority of experiments are performed by using immortalized microglia-like cells or primary microglia prepared from pre- or postnatal rodent brain. As those may not adequately reflect the microglial biology in the adult brain, this protocol advocates a procedure which allows for the isolation, purification, and subsequent analysis of microglial cells. Once isolated, the principal state of activation, M1 or M2, can be determined in adult microglia using fluorescence-activated cell sorting, quantitative PCR, and/or Western blotting. Likewise, adult microglia generated by this protocol can be used for functional analysis through cell cultivation for a limited time.