A precision made device to aid in hand trimming resin tissue blocks to the desired shape for ultramicrotomy. The knurled knife guide swivels to help the trimming blade to cut the sides of the block. May be utilized with any stereomicroscope with epi-illumination. The trimmer is supplied with a standard chuck to accommodate the block size 00. (Stain Technology, Vol. 49, No 4: pp. 129-132, 1974)