In isoelectric focusing systems--a technique widely used for separation and characterization of proteins--the value of the volt-hour integral required to achieve steady-state focusing conditions differs markedly for different proteins. A convenient method to measure the correct volt-hour integral for a given protein, thereby assuring intra- and interlaboratory reproducibility of experiments, can be performed with a volt-hour integrator. As commercially available integrators are compatible only with the power supply marketed by the same manufacturer, a volt-hour integrator was designed which can be used in conjunction with any commercial or homemade power supply. This simple, low-cost integrator is expected to be of interest to those researchers who have so far refrained from introducing volt-hour integration, due to incompatibility of commercial volt-hour integrators with their isoelectric focusing system.