What is the difference between Zymography and SDS-PAGE?

The purposes of SDS-PAGE and zymography are substantially different—while SDS-PAGE is largely used to determine the molecular weight of proteins, zymography is used to determine enzymatic activity. In addition, proteins are fully denatured when performing SDS-PAGE, but with zymography, proteins undergo renaturation due to the absence of any reducing agents, and in that way retain enzymatic activity.