To investigate the effect of lithium carbonate on normal volunteers' moods, we randomly assigned 30 subjects to 5 weeks each of placebo and lithium treatment with crossover at midstudy. Lithium levels were maintained during the treatment period at a mean serum level of 0.54 mEq/L. All subjects completed visual analogue mood scales (VAMS) daily throughout the study period; segmented visual analogue scales (SVAS) measuring mood, anxiety, and energy and the Profile of Mood States (POMS) were completed weekly at testing sessions. Neither mean mood nor mood variability as assessed by the delta square (mean square successive difference) differed between placebo and lithium conditions. Segmented visual analogue scale mood ratings were highly correlated with the VAMS and similarly showed no difference between conditions. The self-rated mood variability, however, declined significantly in both experimental conditions as a function of time on study. None of the POMS factors differed between placebo and lithium conditions. These data suggest that lithium, in modest doses administered over 5 weeks, does not have a substantial mood-stabilizing effect in normal subjects.