Abstract: An actuating mechanism for sequentially advancing and retracting a lancet needle includes a carriage for carrying the advancement and retraction of the needle, and a cam-following structure for transmitting propulsion to the carriage during the advancement. The actuating mechanism is also provided with a drive cam structure which engages the cam-following structure to direct the advancement propulsion. The cam-following structure can have a separate surface engagable with the drive cam structure during the retraction of the carriage and during arming of the actuator for the advancement propulsion.