[en] Multicell spheroids provide an in vitro tumour model of intermediate complexity between tumours and standard cell cultures. They contain radiation resistant, chronically hypoxic cells which develop spontaneously as the spheroids grow, and exist in a tumour-like environment, yet retain their growth potential. Changes in radiosensitivity of cells in spheroids were demonstrated due to intercellular contact, cell cycle redistribution and hypoxia. Cells grown in close contact had an enhanced capacity to accumulate and repair sublethal damage. When maintained in close intercellular contact during the colony formation, the cells had an increased radiation resistance. Chronically hypoxic cells could be sensitized by the electron affinic, oxygen mimic chemicals. Chemotherapeutic responses of both cycling and noncycling cells can be studied concurrently in three-dimensional contact in the tumour-like environment of spheroids. Selective killing of cycling and noncycling cells occurred after treatment with hydroxyurea and metronidazole, respectively. These results suggest that the spheroid tumour model will be useful for studies of combined modalities of therapy