AbstractThe relativistic forms of collision free Boltzmann equation as proposed by Taub, Clemmow&Willson, Linhart and Ken‐iti Goto are investigated from the point of view of their mutual relationship. It is shown that the most exact forms, given by Taub, Clemmow&Willson and Linhart, are completely equivalent, while Ken‐iti Goto's version is restricted to the case of four power free for