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At present, superconducting filters are usually tuned using screws, but there are many reasons to seek an alternative. Laser trimming is an attractive choice. A laser trimming system is described that can tune a high temperature superconductor microstrip filter while it is cooled and connected to a network analyser. Software has been written to control the system, fit measured data and modify a filter design to account for unintended couplings. The residual material left after trimming YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// has been shown to have negligible microwave loss. The system has been used to tune a simple three-resonator filter.