An introductory review of hardware aspects of on-line experimental data processing reveals that the combination of a specialized (hard-wired) preprocessing unit coupled with a programmable laboratory computer is an optimal set up for an electrophysiological laboratory. The paper deals with a proposed modular system, which makes the assembly of a large number of different preprocessing units possible. Some practical applications of the preprocessing units coupled with a LINC (D.E.C.) computer are presented in conclusion.