Abstract: The mixing of materials pre-packaged in precise amounts in separate vials. Use is made of an adaptor of resilient material in which a pair of vials are releasably engaged in sealing relation, in end-to-end relation, with a communicating passage therebetween. The assembled adaptor and vials can be shaken to effect the desired intermixing of the materials present in the vials without loss of material or contamination. Thereafter the mixture can be located in one vial and the adaptor separated from the vials for re-use.