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An uniform-field argon-filled gas proportional scintillation counter, using a large-area avalanche photodiode, is presented. The excitation and ionization thresholds for argon were found to be approximately 0.7 and 3.7 V cm/sup -1/ torr/sup -1/, respectively. An upper limit of 0.30/spl plusmn/0.04 was measured for the argon Fano factor for 5.9-keV X-rays. An energy resolution of 12.5% full-width-at-half-maximum was achieved for 5.9-keV X-rays. The ultraviolet large-area avalanche photodiode proved to be suitable for reading the scintillation light of an argon-filled gas proportional scintillation counter, providing a quantum efficiency of about 50% at 128 nm. Good photodiode performance is already achieved for gains about 100.