Assuming an electron temperature T = 10 4 °K and an electron density N e = 10 4 cm −3 , which are typical values for planetary nebulae, the level populations of hydrogen are calculated allowing for: radiative capture and cascade ; collisional ionization and three-body recombination ; collisional n → n ±1 transitions. It is only for large values of n , n ≳40, that the level populations differ significantly from those obtained in the usual radiative theory. Whereas the radiative theory predicts a sharp drop in intensity on the long wavelength side of the Balmer limit, the present theory predicts a more gradual decrease, extending over about 5 Å. This effect should be clearly observable on high dispersion spectra.