[en] A detailed analysis of an integral transport theory of electrons and ions in a gas in a field is presented. Different procedures allowing, in principle, the rigorous calculation of velocity distribution, drift velocity and diffusion coefficients are discussed. A derivation of a general expression for the transition probability, from a given velocity to another, which holds for any kind of collision, is given. Some questions linked to the convergence of iterative procedures of solution of some basic integral equations are also treated. (author)