1 code 693, NASA/GSFC,Greenbelt, MD 20771, USA

2 CRAAM, Instituto Presbiteriano Mackenzie, Rua da Consolação 896, 01302-000 São Paulo, SP, Brazil

3 Code 661, LHEA, NASA/GSFC, Greenbelt, MD 20661

4 Observatoire de Paris, Section de Meudon, DASOP, CNRS-UMR~8645, F-92195 Meudon, France

The most energetic electron-dominated flares should produce observable levels of synchrotron emission in the far-infrared (IR) spectral region, from electrons in the 20-80 MeV range. Relatively modest IR instrumentation would be capable of observing this emission with good sensitivity on a 30 milli-second time scale. The possibility of investigating relativistic electron acceleration on such rapid time scales may provide the most severe constraints on particle acceleration theories. Appropriate far-IR and submillimter flare observations will therefore be extremely complementary to HESSI. We will discuss the prospects for making such observations from space or utilizing a sub-orbital experiment, and from the ground using the new Solar Submillimter Telescope (SST).