Microglia and astrocytes are major glial cell types in the central nervous system (CNS). Under normal conditions, they play a variety of supportive and protective functions, but when inappropriately stimulated by excessive or chronic stimuli, they can become detrimental to CNS health, both in their own effector functions and by orchestrating inflammatory processes. Microglia and astrocytes both produce matrix metalloproteinases (MMPs), which play important roles in physiological and pathological processes. To characterize MMP expression in glial cells, and to gain insights into the roles they play in regulating tissue repair and remodeling, we employ the method of gel zymography to quantify levels of MMP-2 and MMP-9, as well as their inactive pro-forms. This technique is relatively easy and simple to perform and provides quick and quantifiable data. In this chapter, we describe this approach to analyze MMP expression in supernatants from primary mouse cultures of microglia and astrocytes.