Most recent papers on sparse matrix methods in circuit analysis are written to describe large problem capability, but usually the illustrations given are for relatively small problems. In this paper a computer program for frequency domain analysis of largeRLCMnetworks is described. It is regularly used on 3000-4000 node networks with many large sets of mutually coupled inductors. Timing and storage figures are given for a 3300 node problem. In the first part, the generation of the admittance description for networks with mutual inductors is described. Then the sparse matrix techniques are discussed. Some are standard, but the unique use of storage utilized in the construction of theLUfactorization makes it possible to solve very large problems in a reasonable amount of core storage and time.