A device for mixing biological specimens contained in flexible storage bags (104) at controlled temperature, comprising a support (105) for supporting a storage bag containing a biological specimen to be mixed; means for imparting a displacement to a specimen in a storage bag on the support to mix the specimen; and temperature control means for maintaining the specimens at a controlled temperature during mixing. The means for imparting displacement to a specimen comprises at least one inflatable/deflatable bag (102, 103) (air bag) that when inflated contacts the surface of a part of a storage bag to progressively squeeze the storage bag and displace the contained specimen into another part of the storage bag.