[en] HeLa cells were irradiated at liquid nitrogen temperature with negative pions from Nimrod at the Rutherford Laboratory and then assayed for survival of colony-forming ability. Complete dose-response curves were obtained from repeated determinations at 14 different positions along the depth-dose profile and survival curves were fitted to the data by computer programme. A depth-damage profile was thus established in terms of the final slopes of these survival curves. This confirmed the expected RBE value of 1.84 relative to x-rays at the ionization peak. Although a value of unity was found in the main plateau region, the ''entrance'' positions showed significantly higher values. (author)