This chapter addresses the characteristics and spatial distribution of intracellular potentials, the spread of paroxysmal depolarization shifts (PDSs) through the cortex, the extracellular field potentials in three dimensions, and the concentrations of penicillin in direct contact with elements in the epileptogenic focus. Data are presented that show that there are several types or gradations of PDS intensities within each focus; PDS types are distributed in groups related to their distance from the center of the focus and to the concentration of the epileptogenic drug; the morphology and repetition rate of electroencephalogram (EEG) spikes are related to features of the intracellular potentials; a mathematical model can estimate the distribution of concentrations of penicillin within the focus over long periods; no barriers impede diffusion of penicillin either at the cortical surface or at the boundary between gray and white matter; the potential field of the EEG spike is defined in three dimensions; and PDSs spread through the focus at the rate of 0.25 m/sec.