The theoretic framework of electrode systems and numerical data for use in serum analysis is given. Original literature and recent applications to serum analysis are compiled for different types of sensors. The interactions of various effects and their relevance in the context of the precision that newer instrumentation offers are discussed. Specifically, the following topics are treated: response to interfering ions (Nicolsky Eq.), concentration to activity conversion (Debye-Hückel formalism), and liquid-junction potentials (Henderson Eq.); Debye-Hückel parameters, selectivity factors, and physiologic activity ranges; solid-state, liquid-membrane, and special electrodes; flow-through systems, precision, and stability.