Activating region I of GAL4 has been defined as a region 48 amino acids long which, when attached to GAL4's DNA-binding domain, activates transcription in yeast. Here we describe mutants bearing changes in and around this highly acidic activating region. We find mutations that increase the activation function invariably increase the acidity of the region and some but not all of the mutations that decrease the activation function decrease the acidity of the region.