  The oldest stars hide information about the chemical evolution of the early
universe. In this contect new models of the AGB stellar evolution phase at very
low and zero metallicity are presented. Due to the deficiency or absence of CNO
catalytic material hydrogen burning operates at significantly higher
temperatures than in stars of higher metallicity. As a result convective mixing
plays a very important role since the nuclear burning shells are not well
separated by an entropy barrier. These stars can host flash-like burning events
induced by mixing of C12 and protons at the core-envelope interface. Three
different mixing events with proton-capture nucleosynthesis can be encountered.
One of them, the hot dredge-up, is reported here for the first time. All these
specific modes of nucleosynthesis are relevant for the production of CNO
material in the first intermediate mass stars.
