An investigation was made to find out the importance of gugulu (Commiphora mukul) in thyroid function of mice and to reveal the possible involvement of lipid peroxidation (LPO), if any. While no marked change in the concentrations of serum thyroxine (T4) was observed, triiodoth yronine (T3) concentration and T3/T4 ratio were enhanced following the administration of gugulu extract (0.2 g/kg b. wt./d for 15 days). A concomitant decrease in LPO was also noticed in liver, the principal site of T3 generation, suggesting that gugulu induced increase in T3 concentration is LPO mediated.