Growing, cutting, and handling Avena coleoptiles in total darkness is a prerequisite for studies on the influence of small quantities of light on the production of auxin by isolated coleoptile tips. A technique is described for putting coleoptile tips on agar without exposing them to any light before and during handling. The plants are selected in darkness by touch, their coleoptiles are isolated and the primary leaves removed, both also by touch. Then the coleoptiles are put in a cutting apparatus as described by van der Weij (1932) with the improvements made by Huisinga (1964) (fig. I). The centres of the holes through which the coleoptiles are passed are at a distance of 2 mm. The coleoptiles are fixed with their tips aligned with the foreplate and subsequently advanced 1 mm by turning the screw once (depending on the speed of the screw). Tips of one mm can now be cut off by sliding a razor-blade with thickened back over the foreplate. By advancing the blade between two ledges the tips come onto the blade always in the same position.