This paper considers the use of two types of gamma detector for the in-situ assay of plutonium contaminated materials (PCM): the thin sodium iodide FIDLER (Field Instrument for the Detection of Low Energy Radiation) and the HPGe (High Purity Germanium) detector. The difficulty of the accurate assay of PCM in the past has led to a default mechanism of collecting such wastes in drums, or other types of containers, for subsequent assessment. This has resulted in many thousands of such drums being collected and stored on the major UK sites which were involved with the handling and processing of plutonium. In some cases these drums have been stored for over 20 years. This paper gives a description of the current technologies for monitoring these stored wastes, but more importantly proposes that it would be a better practice to measure such future PCM wastes in-situ, before any demolition or decommissioning is undertaken.