The aim of this study is to examine biological behaviour of radiolabeled guanine with [Tc(CO)(3)](+) core in vitro and in vivo. In vitro biological behavior of Tc-99m(CO)(3)-Gua was evaluated on Lung (A-549), Breast (MCF-7), Colonic (Caco) carcinoma cell lines and normal human bronchial epithelial (NHBE). Tc-99m(CO)(3)-Gua compound showed high uptake on A-549 cell line when compared to NHBE cell line. Biodistribution characteristics of Tc-99m(CO)(3)-Gua was evaluated using New Zeland Rabbits. Scintigraphic results showed that a high level of radioactivity was observed in the lungs and liver shortly after administration of the Tc-99m(CO)(3)-Gua and excretion takes place via both renal and hepatobiliary route. It was concluded that Tc-99m(CO)(3)-Gua could be used as a nucleotide radiopharmaceutical for imaging purposes.