The influence of convection and interfacial-reaction resistance on the response of microsensors, including the effects of : (i) fluid no-rv rates; (ii) reactant (to be sensed) concentration and diffusion coefficient; (iii) fluid conduit and microsensor size; and (iv) sensor potential and interfacial-reaction resistance, are clarified. For steady-state convective diffusion to a microdisk sensor, it is shown that sensor response is a monotonic function of two dimensionless groups : the Peclet number Pe, which characterizes the magnitude of convective transport relative to that of diffusion, and the group tan (theta), which provides a measure of diffusive-transport resistance relative to that of the interfacial charge-transfer reaction. A singular-perturbation solution provides the sensor response vs. Pe and theta for small Pe, corresponding to slow fluid flows and small disks, and numerical calculations extend the analysis to higher Pe values. The analysis suggests a method for increasing the signal-to-noise ratio through altering the sensor bias potential.