Abstract: A box-like outer enclosure with flat clear rigid plastic walls forms an environmental chamber designed for a high-risk newborn infant. A flexible tubular membrane of clear plastic open at both ends optionally forms an inner enclosure for an infant within the chamber and is attachable at one end to an endwall of the chamber. A flat two-piece clear plastic lid slidable along the top edges of the outer enclosure's sidewalls provides top access to the chamber at its center and both ends. The lid is held in place without restricting its sliding movement by spring clamps. Legs on the outer enclosure elevate it above a supporting platform and are attachable to such platform. A breathable gas circuit including a heater with a fan forces a variable and humidified mixture of air and oxygen at a controlled temperature and flow rate into the chamber through an endwall intake opening provided with vertically oriented vanes. The gas is discharged from the chamber through an opposite endwall exhaust opening.