A unit is described to regulate the electrical power delivered to an isoelectric focusing cell. The device consists in a resistance set, in series with a power supply, which can be adjusted to a suitable resistance value in order to permit only minor changes in wattage. Simultanoeus monitoring of voltage and current is also carried out with a pen-recorder adaptor. The improvements in operative conditions achieved by these means are tested by the fractionation of mammalian growth hormones.