Though positron emission tomography (PET) has attained a rightful place in the vanguard of nuclear oncology imaging there is still much that can be done using single photon tracers. Whether or not it is the use of general agents such as (201)Tl or receptor targeting using somatostatin analogues many cancers and the processes involved with them are still best seen with g-emitting radionuclides and gamma cameras. This article reviews the scope of using these tracers in oncology and emphasises that in nuclear oncology we are as much concerned with the questions as what the cancer is doing and how can be exploit differences between the cancer and normal tissue to aid diagnosis. The advent of new radionuclide therapy techniques will mean that preassessment with diagnostic agents will increase the need to have high quality single photon imaging. New receptor systems such as those using gastrin and bombesin are being developed. We can also use (99m)Tc based agents to identify hypoxia in cancer, angiogenesis and apoptosis. For those who are interested in the biology of cancer and interested in exploiting this for treatment will find that there is still much that can be done without a PET scanner and normally at a lower cost. About this issue, it is important to consider the recent development of dual-modality integrated imaging systems (SPET/CT) that allows to co-register the acquired images by means of the hardware in the same session. These new devices have a particular added value in tumour imaging since they provide the exact localisation of lesions and exclude some non correct interpretations of the physiologic uptakes for SPET findings. In addition there are many evidences that the fused images can give additional information in the diagnostic work up of patients by improving the accuracy of single photon scintigraphy. These new technologies lead to a continuous optimisation in the quality of imaging and contribute more and more to integrate the nuclear medicine modalities in the clinical management of cancer diseases.