A novel, inexpensive apparatus (locometer) was designed to measure behavioral activity of rats including gross locomotor activity, rearing, and structural characteristics of movement patterns (i.e. fractal dimension). Measurements were done in 3 dimensions at a resolution of approximately 1 cm. To test the sensitivity and specificity of the system, saline or D-amphetamine (0.5, 1, 2, and 4 mg/kg, i.p.) was administered to rats and locomotor activity, rearing and the structure of motor behavior calculated as the fractal dimension, were analyzed. The results obtained with the locometer were consistent with previous reports using other devices to measure basal and stimulant-induced behavior (i.e., infrared photobeam, visual observation, video tracking, etc.). Based on these data, the novel apparatus, described herein, provides a sensitive, versatile, and inexpensive tool for the analysis of locomotor behavior in the rat.