Abstract: A tissue cassette holder including a rectangular open-top tray having a pair of locking side rails affixed to the upper portion of the longitudinal sides thereof, the rails having a raised elastomeric protuberance projecting inwardly from the center thereof and spaced sufficiently apart to permit a conventional tissue cassette to snap firmly therebetween. Preferably, the trays are configured to permit removably locking a plurality thereof into superposed and/or side-by-side relationship, and further to positively lock a plurality of cassettes within each such tray for liquid processing and to break such cassettes loose after the tray and cassettes are wax-dipped preparatory to slicing the tissue therein for microanalysis.