The quantum approach to the theory of endoergic associative ionisation reactions of atoms within the framework of the multichannel quantum defect method taking account of configurational interaction between the Rydberg and valence dissociative states is developed. It has been shown that the total cross section of the AI reaction near the ionisation threshold is proportional to the energy E measured from the ionisation threshold ( sigma _AI approximately E). The effect of the resonant quasidiscrete valence states on the ionisation spectrum is studied. As an example, the AI cross section for the reaction N+O to NO⁺+e^- is calculated. The temperature dependence of the AI thermal rate coefficients over a broad temperature range has been considered. The effect of a strong monochromatic radiation field on the AI reactions has been discussed.