This study has been investigated the potenial of increased dietary cysteine to alter the effects of cadmium and lead on tissure and bone metal concentrations, excretion and tissue metallothionein(MT) concentrations. Fifty-four male rats of Sprgue-Dawley strain weighing 149$pm$17g were divided into 9 groups according to body weight. Nine experimental diets with different cadmium (0ppm, 400ppm), lead(0ppm, 710ppm) and cysteine (0.06%, 0.45%, 0.90%) levels were given to rats for 30 days ; Food intake, weight gain, F.E.R, and weights of liver, kidney and femur were decreased in cadmium supplied groups than in cadmium free groups. Urinary and fecal cadmium excretions were increased and MT synthesis we induced in liver, kidney and small intestine in cadmium supplied groups. In lead supplied groups, weight gain and F.E.R were decreased. With cysteine supplementation in cadmium supplied groups, weight gain and F.E.R, and weights of liver, kidney and femur were increased. Cadmium excretion in feces and MT concentrations in liver and kidney were also increased with cysteine supplementation. In lead supplied groups, there was no significant increase in food intake, weight gain and F.E.R with cysteine supplementation. Lead excretion in feces was increased in cysteine supplemented groups. In conclusion, effect of cadmium administration was more toxic than lead adminstration. Cysteine alleviated cadmium and lead toxicity by increasing metallothionein concentration and fecal excretions of heavy metals. Especially, effect of cysteine supplementation was more effective in cadmium groups than in lead groups. Effect of cysteine supplementation was not different with level of cysteine supplementation in both cadmium and lead groups.