The small-signal subthreshold response of the excised squid giant axon to an internal point source of current is oscillatory and propagates with decrement at a velocity close to the spike velocity. The classical electrotonic response, described mathematically by the cable equation and demonstrated by the RC ladder network (Hermann's model), obtains when the membrane potential is equal to the e.m.f. of the potassium current, a condition which is rarely satisfied in the excised giant axon. Experimental data and computations based on the "standard data" of Hodgkin and Huxley are presented. © 1972 Springer-Verlag.