  Pion condensation is studied at one--loop level and nonzero baryochemical
potential in the framework of two flavor constituent quark model using the
one--loop level optimized perturbation theory for the resummation of the
perturbative series. A Landau type of analysis is presented for the
investigation of the phase boundary between the pion condensed/non-condensed
phases. The statement that the condensation starts at $\muI = m_{\pi}$ is
slightly modified by one--loop corrections. The second order critical surface
is determined and analysed in the $\muI-\muB-T$ space. The $\muI$ dependence of
the one--loop level charged pion pole masses is also studied.
