There is described an apparatus for loading test tubes (1) in conveying devices (6) included in an automatic conveyor (7) for test tubes, comprising a recruiting device (2) for test tubes adapted to feed test tubes to a positioning device (4) for test tubes having a lane (15, 16) consisting of two spaced, parallel walls (17) on the edges of which respective motorized belts (18) slide, the distance between said walls (17) forming the lane (15) being adjustable and such that a test tube makes a 90° rotation when horizontally falling from the recruiting device (2), thus remaining vertically hanging and resting on the belts (18) by the projecting part of the cap with respect to the lateral body of the test tube. The belts (18) convey the test tube to a loading area (8) where the test tubes are handled by a test tube handling device (5) to a working point (9) included in the conveyor (7) adapted to automatically convey test tubes from and to modules for preparing and analyzing biological material.