A set of Fortran subroutines is described that enables Butterworth, Chebychev or elliptic filters having a lowpass, highpass or bandpass response to be designed and implemented in a form ready to filter a data sequence with only three lines of user-written program. The software is modular in that separate routines are used for the functions of transfer-function computation, network synthesis and filter simulation. This approach leads to several advantages, which include the ability to implement multiple filters simultaneously. The existence of gerneralised algorithms for network synthesis and simulationenables this filtering facility to be used without knowledge of digital-filter theory.