In the case of a criticality accident, there are two radiation components, i.e. neutron and gamma, and the exposure is heterogeneous. The available techniques are biophysical techniques, which can give data about the dose distribution and the neutron component dose, classical techniques (electroencephalography, lymphocytes counting, dicentric and acentric fragments counting, biochemical indicators) which can give an estimation of the mean biological dose, new biochemical parameters which are good indicators of vital prognosis and new cytogenetic techniques under study. Biological dosimetry or rather research of biological indicators of irradiation remains difficult, particularly because of the heterogeneity of exposure. A multiparametric determination seems the only solution.