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Root-length measurements are an important aspect of many agronomic research programs. Several automated systems have been reported which use modifications of the line-intersect technique to estimate root length; however, most of these systems are very costly. This paper describes an inexpensive automated system using a modified line-intersect technique to estimate root length. An X-Y plotter was used to move a light sensor in a grid pattern through the projected photographic image of a root system, recording intersections with an event counter. Compared to manual counting using the Line-intersect technique, the system described accurately estimated root length of samples up to 10 m in length (r2 = 0.98). The advantage of our system is that costs are reduced by using equipment that is readily available at most laboratories: X-Y plotter and slide projector. The cost of additional items was less than $600. Each determination of root length required 50 sec. The accuracy of the system was comparable to others that are based on the line-intersect technique.