Laser microprobe mass spectrometry (LMMS) detection limits for mercury have been determined using mercury-doped Spurr's tissue embedding medium. Actual mercury concentrations were confirmed via INAA. Procedures have also been developed to measure lithium and indium concentrations in thin films of polymerized Spurr's samples via PIGE and PIXE. These elements are currently being investigated as laser power density internal standards in the analysis of human tissue for studies of trace element involvement in neurological diseases.