Mathematical models, programmed on a computer, were developed to simulate voltage decrement within the transverse tubule system of skeletal muscle; and the effect on the measurement of the properties of the K inward rectifier. Three models were produced to investigate particular facets of the phenomenon. i) A steady state model, using a non-linear iterative solution for the TTS voltage decrement, was used to generate conductance-voltage curves and the current variance of fluctuations about the mean current. The K inward rectifier was modelled as a population of channels, with a voltage dependent open state probability described by a Boltzmann equation. ii) A finite difference model of the TTS voltage distribution was used to provide a more realistic simulation of the time and voltage dependence of the K inward rectifier properties as modified by voltage decrement. The K conductance had both an instantanous voltage dependent component and a time dependent relaxation with 1st order kinetics. iii) The TTS network acts as a low pass filter on, channel generated, current fluctuations within the TTS wall membrane. The filter passband of this network was investigated using an AC circuit analyis program. The results from the above models showed that the K inward rectifier, measured in fibres in bathing solutions with a high K ion content (120 mM) is subject to distortion by TTS voltage decrement. However, measurements of the unit K channel conductance in the voltage range, -10 mM to -20 mV, can be made without significant error. The channel density, on the other hand, can only be obtained after correction is made for voltage decrement error. The voltage decrement error in measured fibre current, conductance, capacity, and the voltage dependence of the conductance were also quantified.