This paper describes the measurement of the plasma parameters in an 8-metre long theta pinch. The plasma in the midplane is found to be free of end effects and energy loss for some tens of microseconds and is characterized by electron densities of 2 - 5 × 1016 electrons/cm3 and temperatures of 100 - 300 eV. The measured radial distributions of temperature and density and their dependence on voltage and filling pressure were in agreement with MHD code calculations using an anomalous resistivity previously shown to account for the diffusion in the early stages.