Abstract: A bag arrangement for intermixing two, separately stored substances. The bag arrangement includes a bag having a jacket defining an inner chamber for accommodating a first substance and a piercing device having a chamber in which the jacket is received. A single piercing member is provided on one side of the jacket and a hollow abutment is located opposite the piercing member on an opposite side of the jacket and forms a receptacle for accommodating a second substance. Upon actuation of the piercing device, the piercing member pierces the opposite sides of the jacket providing for intermixing of the first and second substances.