Microminiature active filters have been constructed using a combination of thin film and integrated circuits. The advantages of such an approach are discussed. The filter required could be met by a fifth-order Chebyshev function and the method of realization was to split the transfer function into quadratic and linear factors with each factor then realized separately. The tolerances required have been examined using a Monte Carlo computer program and the results are discussed. A filter constructed for use in p.c.m. systems is described.