HST spectroscopical observations of 8 HII galaxies are reported. Ly alpha emission was detected in 4 of them. We find that the velocity structure of the gas is the main determining factor for the escape of the Ly alpha photons, and not the abundance of dust. The rest of the sample shows broad damped Ly alpha absorption attributed to large HI column densities, that is static with respect to the emitted Ly alpha photons, emerging from the HII regions. The star-forming galaxies IZW18 and even more SBS0335-052 may have extremely metal deficient HI clouds, the latter with [O/H] as low as -7.2.