The problem of calculating the impedance of a finite length solenoid immersed in a multiregion cylindrical structure is examined. The transmission line modelling technique is introduced to deal with a large number of regions in a simple and routine way. Bessel functions are completely avoided by replacing each region equivalent T.L. by a cascade connection of elementary T-circuits. The input impedance calculated for a finite length solenoid which was either air-cored, or closely encircling an infinitely long conducting cylinder, was found to agree closely with published values.