Thorleaf Research, Inc. proposes to develop a miniaturized in situ atmospheric probe sampling inlet system for measuring chemical and isotopic composition of the atmospheres of the giant planets, with special emphasis on NASA needs for missions to Uranus and Saturn. Our innovative design will provide a constant flow rate of sample to the inlet of a mass spectrometer (MS) in spite of more than a hundred-fold variation in external atmospheric pressure, allowing the detection sensitivity of the MS to be optimized over the full descent profile of the atmospheric probe, unlike previous sampling systems that depended on fixed leaks. This addresses a key technology gap for planetary studies, mainly how to acquire and prepare samples for in situ analysis while meeting challenging mass, volume and power constraints. Based on our analysis, we project a system mass on the order of 0.5 kg and an average power consumption of <0.5 watt, depending on materials and the configuration selected. The goal of our proposed SBIR Phase I effort is to demonstrate feasibility for a miniaturized in situ atmospheric probe sampling inlet system for Uranus and Saturn, and to develop a detailed design for fabricating prototype instrumentation in Phase II.