Abstract: A dilution bottle for mixing a sample material with a sterile diluent solution. The bottle comprises side wall portions of synthetic polymeric material formed around the central axis of the bottle, a bottom wall of polymeric material closing off one end of the bottle, and the opposite end of the bottle including an opening. At least one side wall portion of the bottle is formed with one or more concave protrusions extending into the interior of the bottle, the protrusions being dimensioned so as not to obstruct the introduction of insertion means along said axis. The bottle also includes means for sealing the opening of the bottle so as to maintain aseptic conditions within the bottle.