Adult and weanling rats were used in two studies which investigated the ti.me course of and developmental differences in the toxic effects of a single i.p. injection of LiCl. The studies examined LiCl' s effect on food reinforced bar pressing, open-field behavior, water intake, and taste aversion learning. Both experiments used a 2 x 3 x 21 mixed design which provided for the factorial combination of adult and weanling age groups with three injection conditions, 1.2 mEq LiCl, 3.0 mEq LiCl, and isotonic saline, and 21 test trials over a period of 2 1/2 hours. Experiment 1 demonstrated that LiCl reduced rates of bar pressing. Numerically, weanlings showed the maximum toxic effects later and recovered earlier than adults, but the age difference was not significant. Data from the open-field observations were factor analyzed; analysis of variance on the resultant factor scores showed significant drug effects for only one of four common factors. The factor showing significant results correlated most highly with lying down in the open-field and numerically but not statistically indicated that weanlings exhibit an earlier but less intense effect of LiCl injection relative to adults. Overall the behavioral effects of LiCl were strongest from 8 to 28 minutes post injection and were essentially absent after 2 1/2 hours. LiCl was shown to reduce fluid intake with the reduction being less for weanlings than for adults. LiCl injection produced taste aversions in all groups, both ages showed equilivant levels of aversion. / Master of Science