[en] During in vivo measurements, particularly of doses to patients undergoing total body irradiation, considerable differences are often found between results obtained with semiconductors and thermoluminescent dosemeters. The two types of detector were compared with an ionization chamber at a series of depths including both build-up and build-down regions. Measurements of variation in sensitivity with dose and dose rates were also made so that these could be eliminated from the results. Measurements were made with the 6MV linear accelerator used at Leicester for total body irradiation. (author)