[en] The impact of neutral particles on the H mode transition power threshold is addressed in this paper. The fact that the compiled threshold database form various tokamaks has not yet been successful in providing a unique and reliable threshold power scaling is mainly ascribed to the ambiguities due to size and density dependences. In particular, the density dependence is regarded as the most crucial issue, which is, however, also most difficult to analyze, because of its sensitivity to the wall conditions. On the basis of the results of experimental investigations on JT-60U, it was established, first, that the edge neutral particle density determines the degree to which the threshold power depends on the density, and, second, that the density boundary below which the H mode transition cannot occur may also be governed by the edge neutrals. Therefore, information on the edge neutral particles can integrate the different density dependences observed in various tokamaks, and thereby a firm basis for size scaling may also be established, which may, to an adequate accuracy, also be extrapolated to a fusion reactor. (author). 12 refs, 5 figs