Objective: To make comparison of the weight in grams (mean body weight, absolute renal weight and relative renal weight) of the albino rats after treatment with Lithium carbonate and L-Arginine. Design: A prospective experimental study. Place: Department of Anatomy, Basic Medical Sciences Institute, Jinnah Post Graduate Medical Centre Karachi Duration: July 2007 to November 2007 Methodology: Forty five adult albino rats of either sex were taken and divided into three groups as A, B and C which were further subdivided into three subgroups according to the period of treatment they received i.e. two, four and six weeks respectively. Animals were weighed before the commencement of study. Group 'A' animals served as control and Group 'B' animals received lithium carbonate (Neurolith, Adamjee Pharma) in a dose of 20 mg/kg/day with feed. Group 'C' animals received lithium carbonate 20 mg/kg/day with feed and L-Arginine (Arginine, General nutrition corporation, Pittsburg USA) 300 mg/kg/day with feed. At the end of period of treatment animals were again weighed and then sacrificed. The kidneys were removed and their weights were recorded. Results: Comparison showed an insignificant (P>0.05), significant (P<0.05) and highly significant increase (P<0.001) in body weights in subgroups, A1, A2 and A3. The significant (P<0.05), moderately significance (P<0.01) and highly significant decrease (P<0.001) in body weight were noted in subgroups B1, B2and B3 when they were compared with themselves and highly significant (P<0.001) results were obtained when they were compared to control. Subgroups C1, C2 and C3 showed insignificant (P>0.05), significant (P<0.05), moderately significance (P<0.01) increase in body weights when compared with themselves and insignificant results were obtained when compared to control. Absolute kidney weights showed significant increase (P<0.05) in subgroup B1. Moderately significant (P<0.05), and highly significant decrease (P<0.001), results were found in subgroup B2 and B3. Relative kidney weights were found increased in lithium treated subgroups. Conclusion: The lithium carbonate treated rats show significant (P<0.05) weight changes. Insignificant (P>0.05) results are obtained with concomitant administration of L-Arginine with Lithium carbonate.