Abstract: A sample transport mechanism is disclosed for conveying test tube samples in an endless path to and then away from a test station. The samples are removably inserted into elongated test tube supports arrayed upon a table in two rows and moveable in a rectangular path. Underlying the table is a plate generally coextensive therewith and having brackets mounting pins projecting above the margin of the table above and below the rows. The sample supports have parallel grooves in their bottom surfaces transverse to the longitudinal axis of the supports, and into which the pins may engage. The plate also has two openings, one square and the other rectangular, and into which are engaged cams. The cams when rotated move the plate in a rectangular path with respect to the table. The spacing of the pin and slots is such that the pins normally engage two diagonally opposite corner trays and move them longitudinally toward the next row by the incremental distance separating two adjacent samples.