Abstract: Magnetic device for withdrawing magnetic gel beads or the like from a biological fluid and transferring them to an immunoenzymatic assay medium. This device includes a housing of insulating material, particularly of plastic material, into which is inserted a magnet and over the height of which is formed a traversing orifice in which is housed a rod formed of a lower portion of magnetizable material and an upper portion of non-magnetizable material on which is mounted a return spring, between a stop washer fixed in the vicinity of the upper end of the rod and the upper surface of the housing. The device can advantageously be included in a ready-for-use kit for carrying out immunoenzymatic assays.