The present invention provides an actuator mechanism for sequentially advancing and retracting a lancet needle and includes a drive carriage for advancing and retracting the lancet needle and a hinge structure operatively connected to displace the drive carriage. The hinge structure includes first and second coupled leaf members relatively pivotal between a first position thereof in which the drive carriage is advanced to project and thrust the lancet needle into a tissue penetration position, and the second pivotal position of the leaf members in which the drive carriage is retracted to withdraw the lancet needle from the penetration position. The leaf members can also be pivotal to a third position in which the drive carriage is retracted prior to initiating the advancement so that the first position of the leaf members is pivotally intermediate between the second and third relative positions thereof. The drive carriage is thus advanced and thereafter retracted for thrusting and then withdrawing the lancet needle in continuous reversal motions thereof. The drive carriage is guided so that the advancement and retraction motions are along a highly accurate linear path.