Air removal is completed and ascertained, in steam sterilization systems which use steam flow through a sterilizing chamber to facilitate air removal, by methods which enable steam-table values for a dependent variable relationship of pressure and temperature, as exhibited by confined saturated steam, to be utilized under steam flow conditions.Apparatus for controlling and measuring chamber conditions are provided so that such established steam-table values for confined steam can be readily and reliably used to establish and ascertain complete air removal while steam is flowing through the chamber.In a representative embodiment, chamber pressure is held substantially constant while the remaining variable chamber temperature is measured. Venting of chamber atmosphere is continuous during such control of chamber pressure with chamber temperature being measured until a value is reached corresponding to the steam-table value at the level of the chamber pressure being held.With complete removal of the air ascertained, sterilizing exposure conditions can be established rapidly by substantially reducing venting of chamber atmosphere since any remaining portions of the cycle, whether establishing or maintaining sterilizing exposure conditions, need not be relied on for removal of air.Control apparatus, electromechanical and electronic processor, are provided for automatically completing air removal and ascertaining effective air removal.