Abstract: A .sup.3 He-.sup.4 He dilution cryostat is provided in which a series of concentric dismountable enclosures permit ready disassembly for servicing and sample changing, and in which a secondary pumping circuit and a secondary cryogenic material delivery circuit provide rapid and convenient internal cooling of the dilution chamber by means of cooled cryogenic material, the dilution chamber being subsequently filled with the same cryogenic material in the liquified state. More particularly, the cryostat possesses a primary pumping circuit by which a .sup.3 He-.sup.4 He mixture is forced through cooling elements to liquify it, transferred into the dilution chamber and an associated evaporator, and the .sup.3 He finally recycled.