This article describes the use of Langmuir probes to measure plasma parameters in low density, low temperature plasmas with a strong applied magnetic field. The experiment has been performed at the Physics Department of Milan’s University on the steady-state toroidal machine “Thorello.” Results have been analyzed by taking into account instrumental and ionic sheath effects. Finally, experimental results have been compared with direct measurements of the electron distribution function in Thorello. ©1997 American Institute of Physics.