The present invention relates to methods of conducting assays for enzymatic activity on microarrays useful for the large-scale study of protein function, screening assays, and high-throughput analysis of enzymatic reactions. The invention relates to methods of using protein chips to assay the presence, amount, activity and/or function of enzymes present in a protein sample on a protein chip. In particular, the methods of the invention relate to conducting enzymatic assays using a microarray wherein a protein and a substance are immobilized on the surface of a solid support and wherein the protein and the substance are in proximity to each other sufficient for the occurrence of an enzymatic reaction between the substance and the protein. The invention also relates to microarrays that have an enzyme and a substrate immobilized on their surface wherein the enzyme and the substrate are in proximity to each other sufficient for the occurrence of an enzymatic reaction between the enzyme and the substrate.