  Following the renewed interest for axions as a dark matter component, we
revisit the effects of energy loss by axion emission on the evolution of the
first generation of stars. These stars with zero metallicity are supposed to be
massive, more compact, and hotter than subsequent generations. It is hence
important to extend previous studies restricted to solar metallicity stars. Our
analysis first compares the evolution of solar metallicity 8, 10 and 12
M$_\odot$ stars to previous work. We then calculate the evolution of 8 zero
metallicity stars with and without axion losses and with masses ranging from 20
to 150 M$_\odot$. For the solar metallicity models, we confirm the
disappearance of the blue loop phase for a value of the axion-photon coupling,
$g_{a\gamma}=10^{-10} {\rm GeV}^{-1}$. Regarding the Pop. III stars, we show
that for $g_{a\gamma}=10^{-10} {\rm GeV}^{-1}$, their evolution is not much
affected by axion losses except within the range of masses 80$-$130 M$_\odot$.
Such stars show significant differences both in their tracks within the
$T_c$-$\rho_c$ diagram and in their central composition (in particular
$^{20}$Ne and $^{24}$Mg). We discuss the origin of these modifications from the
stellar physics point of view, and their potential observational signatures.
