Surgical procedures are conducted in a protected environment wherein a laminar flow of micro filtered air is passed from a top to a bottom of an enclosure with transparent panels defining a space for manual access of the surgeon's hands and arms. Air circulation is forced through a high performance HEPA filter between an inlet including the bottom of the enclosure and an outlet at the top, both including panels with an array of apertures for establishing substantially laminar flow. A duct along an endwall of the enclosure carries filtered air to the top. A positive pressure differential is maintained between the inside of the surgical compartment and the outside, to protect the patient operative site from contamination by airborne particles. The enclosure rests on top of a mobile cabinet and has access ports for connection lines and also for bringing the surgical subject into the enclosure. For experimental animals, an access port for cage boxes can be provided. A microscope is movably mounted in the enclosure, with the object lenses disposed outside the enclosure on an extension which can extend through the access port.