  Aims: We investigate temperature fluctuations in H II regions in terms of a
two-phase model, which assumes that the nebular gas consists of a hot and a
cold phase.
  Methods: We derive general formulae for T([O III), the [O III] forbidden line
temperature, and T(H I), the hydrogen Balmer jump temperature, in terms of the
temperatures of the hot and cold phases, T_h and T_c.
  Results: For large temperature differences, the values of t2 required to
account for the observed difference between T([O III]) and T(H I) are much
lower than those deduced using the classical formulae that assume random and
small amplitude temperature fluctuations. One should therefore be cautious when
using a two-phase model to account for empirically derived $t^2$ values. We
present a correction of a recent work by Giammanco & Beckman, who use a
two-phase model to estimate the ionization rate of H II regions by cosmicrays.
We show that a very small amount of cold gas is sufficient to account for t2
values typically inferred for H II regions.
