The EPC-9 computer-controlled amplifier has no front-panel controls; therefore the user interface to the EPC-9 patch-clamp amplifier is defined entirely by software. This paper describes various user interfaces that have been implemented, including a high-level programming interface, a user interface based on the PostScript language, and graphical user interfaces that control the EPC-9 from data-acquisition programs. Also described are the algorithms used for automatic adjustment of the C-Fast and C-Slow transient cancellation circuitry. An overview of the procedures that perform automatic testing and calibration is given.