This paper describes preliminary results in the design, construction, and characterization of cobalt(Il) porphyrins derivatized with alkanethiol appendages. The use of the thiol appendages leads to the formation of a chemisorbed monolayer of the corresponding thiolate at gold electrodes. Our findings suggest that this approach may serve as a beginning for fabricating electrocatalytic monolayers with a preselected architecture through the manipulation of the number and location of the appendages. Voltammetric data indicate that monolayers from both I(Co) and II(Co) catalyze the two-electron reduction of 0 2 to H20 2• The monolayer from I(Co), however, has a lower electrocatalytic activity. Infrared, X-ray photoelectron, and visible spectroscopic data are presented that argue the difference in reactivity arises from a difference in interfacial architecture. The results from attempts to metalate monolayers from I(Hz) and II(H2) support this interpretation. Findings are also reported that indicate the preparation of mixed monolayers (e.g., two-component mono layers from I(Co) and CHs(CH2)aSH) may prove valuable to this area of research.