The purpose of this work was to study the effect of metastatic and non-metastatic mammary adenocarcinoma on tissue distribution of gallium-67 (67 Ga) citrate in Fischer-344 female rats by the use of gamma counting techniques. The homogenate (0.1 mm) of a sample of metastatic and non-metastatic tumor was implanted by subcutaneous injection in the right footpad of each animal's hind extremity. The animals bearing metastatic tumor were studied 2-24 days and the non-metastatic group 2-30 days after the implantation of tumor homogenate. The control group consisted of four animals and tumor-bearing groups of seven to eight animals at each time point. All animals were injected with 1.11 MBq of 67Ga citrate by intravenous administration and sacrificed in halothane anesthesia 48 h later. The relative tissue uptake data are presented as arithmetical mean value with a standard error and graphically demonstrated as normalized data with respect to control. The results demonstrate that 67Ga citrate uptake was largely unaffected in most organs by the presence of either metastatic or non-metastatic tumor. Gallium-67 uptake, however, was significantly and consistently increased in the popliteal lymph nodes of the ipsilateral extremity of tumor implant in the metastatic group. No difference was observed in the non-metastatic tumor group. The findings of this experimental work indicate that the host reaction to the tumor does not modify the gallium uptake characteristics in the normal tissues of tumor-bearing animals.