We describe a new hydrothermal vent sampler, LAREDO, designed to capture hot fluids and incubate them in situ at conditions characteristic of deep-sea hydrothermal vents for periods of hours to days. To accomplish this, LAREDO was engineered to operate at ambient pressures to 6000-m water depth (600bar), in the flow of hot (to 420°C) acidic (to pH of 3) effluent with large particle loads and fast flow rates (>1ms−1). Key features of the LAREDO sampler include the novel application (in this environment) of a torsion bar to generate the energy required to seal the sample chambers, independent and continuous temperature records in two of the three sample chambers, and remote (electronic) or manual (by submersible) modes of closure. Results of LAREDO's first operational field tests on smokers at 9°51′N×104°18′W along the East Pacific Rise indicated successful capture of vent fluid (up to 91% pure effluent by analysis of magnesium content) without leaks after tests of several different instrument configurations. High-resolution temperature records (a datum every 2s for each thermocoupled chamber) indicated achievement of high temperatures (>150°C) in at least one chamber on all dives. The field tests also pointed to simple modifications of LAREDO's design that will improve its ability to monitor the temperature of the captured fluids and to close autonomously on the seafloor. With these improvements and its demonstrated capacity for in situ capture and incubation, LAREDO represents a useful new tool to expand upon biological and geochemical research in the harsh smoker environment.