Abstract: A method for reconstitution of substances includes a liquid container having a pre-determined volume of diluent and a powder container having a corresponding pre-determined amount of powder to be reconstituted. The method allows an individual to safely reconstitute the powder into a liquid solution having the desired concentration without measuring or potential spillage. The powder container includes a female threaded connection designed for liquid-tight attachment to the liquid container and further includes a breakable membrane seal which, when broken by the distal end of the liquid container, creates an orifice for the diluent to enter the powder container to reconstitute the powder and thereafter be displaced into the liquid container for use. Before the membrane seal is broken, the pre-determined amount of powder partially occupies the powder container chamber.