An accurate polynomial expression for the steady-state current in the case of first-order EC＇ reaction is reported using scattering analogue techniques for ultramicro disk electrodes.; When the reaction rate is small, seven terms of diffusion-limited current are reported, and when it is large, five terms of the same are reported. A two-point Pade approximant is derived for all values of reaction rates. By a proper transcription of variables, the methodology is extended to derive chronoamperometric current for diffusion-controlled processes, and excellent agreement with digital simulation data is noticed.