Abstract: Objective : To compare the efficiency and toxication of multiple low-dose (MLD) ¹⁸⁸Re-CL58 and high dose (HD)¹³¹I-chTNT on treatment of cancer. Methods : Patients were treated with MLD of ¹⁸⁸Re-CL58 (or ¹³¹I-Hab18) or HD of ¹³¹I-chTNT. The corresponding efficien-cies and toxications were compared. Results : After treatment with MLD-RIT and HD-RIT, FDG accumulation in lesions was decreased significantly. In some cases, SUV of the micro-metastases were even brought down to the normal line. After treatment with RIT, tumor markers such as CEA also decreased in varying degree, with MLD ¹⁸⁸Re-CL58 more efficient than HD ¹³¹I-chTNT. MLD ¹⁸⁸Re-CL58 affected the immune system positively for it brought down CD₃+ cell and brought up the ratio of CD₄+／CD₈+. MLD RIT induced no visible blood toxication. Both of them had no toxic effect on liver and kidney. Conclusions : MLD RIT were efficient for the treatment of mi-cro-metastasis. MLD RIT partially relief the immune system from suppression, The toxication of RIT was manifested mainly as blood cell inhibition.