Abstract: A blood collection device wherein a double-ended cannula is retracted within the barrel of the device for storage and disposal. The cannula is mounted on a first disc which is connected to a second axially aligned disc by a pair of string-like flexible members which are operable, when the second disc is moved away from the first disc, to retract the cannula completely within the barrel to a position in which the cannula is permanently locked by stopping the first disc against further retractive movement and the second disc against movement toward the first disc.