This study was undertaken to develop the novel radiopharmaceuticals for cancer diagnosis, sentinel lymph node detection (SLND), and brain imaging. Biomolecules have great importance in living systems. Significantly, developed pathway is available for transport and utilization of biomolecules and by taking the advantages of these naturally developed pathways. In this study, the biomolecules like triglycine, 1-azido-1-deoxy-β-D glucopyranoside and folate azide were utilized for various medicinal applications. Biomolecule conjugates were developed by using click chemistryand cyclopentadienyl chemistry (Cp) approach. The spectrophotometric biomolecule complexes techniques. conjugates were were By characterized using radiolabeled the and by using various [ 99m Tc(H 2 O) 3 (CO) 3 ] + evaluated as core, potential radiopharmaceuticals for diagnostic study. The biodistribution of [ 99m Tc(CO) 3 - click-1-azido-1-deoxy-β-D glucopyranoside] and [ 99m Tc(CO) 3 -folate azide] complexes present them as potential tumor scintigraphic agents. Second approach for cancer diagnosis was to radiolabel the anticancer drugs, e.g., 5-fluorouracil and methotrexate with technetium-99m ( 99m Tc) and evaluate them as potential tumor diagnostic agents. Normal biodistribution and tumoral uptake was studied in Swiss webster mice. The results suggest that they might be sucessful tumor diagnostic agents for future use. 99m Tc-5-flurouracil was also applied to the breast cancer patients after getting approval from local ethical committee of INMOL. The sucessful uptake of the drug in tumor tissues with low background ratio presents this drug as a sucessful cancer diagnostic agent. Sentinel Lymph Node Detection (SLND) is of great importance for early stage diagnosis of cancer. All sentinel lymph node imaging agents were studied for their uptake in various body organs, popliteal node, iliac node and popliteal extraction.In this study, we developed rhenium sulfide collidal nanoparticles and xviiiAbstract radiolabeled them with 99m Tc. The sucessful uptake of the drug in sentinel node within 15 min of post injection, presents it as a sucessful candidate for sentinel lymp node detection. Various dextran derivatives were radiolabeled with 99m Tc(CO) 3 and studied for sentinel lymph node detection. The drugs reached the first node within 10 min of post injection. DPZM-8 was the most successful candidate for sentinel lymph node detection among all dextran derivatives studied, so far. 99m Tc-labeled amine thiophene and 99m Tc(CO) 3 -Cp-triglyicne were evaluated as potential brain imaging agents. Amine thiophene is a schiff base which was directly labeled with 99m was radiolabeled with Tc while Cp-triglycine is a biomolecule conjugate which 99m Tc via isolink kit. Normal distribution study in rabbits suggests them as successful candidates for brain scintigraphy.