  We examine the dependence of stellar yields on the metallicity Z of the
stellar population. This effect may be important for the very first chemical
enrichment from Population III stars, at very low Z. In the range of massive
stars, mass loss rates varying with Z have remarkable effects.
  We also estimate chemical yields from Very Massive Objects (from 120 to 1000
Mo), which might have formed more easily in the very low-Z environment of the
first stellar generations.
