Leptin is a protein that is produced primarily in fat tissue and is thought to be a lipostatic feedback signal for the regulation of body fat stores. The purpose of this study was to determine the behavioral specificity of i.c.v.-administered mouse leptin in rats and to assess the effects on meal patterns. Using a modified two-bottle paradigm we examined the putative aversive response to i.c.v. doses of 1, 5, 7, 10, and 30 μg of mouse leptin. Artificial CSF and intraperitoneal lithium chloride served as negative and positive controls, respectively. Saccharin consumption in all leptin treatments was not significantly different from the negative control. Following a recovery period, rats from the same group were used to assess the effects of a 30-μg i.c.v. dose on cumulative food intake and meal patterns using a computer-based system for acquisition of feeding data. Leptin (i.c.v.) significantly increased intermeal interval and decreased meal size. We, therefore, conclude that mouse leptin, at doses up to 30 μg i.c.v., is not aversive in the rat, and that leptin has a multiphasic effect on meal patterns.