Nearly degenerate four-wave mixing (NDFWM) within a closed degenerate two-l
evel atomic transition is theoretically and experimentally examined. Using
the model presented by Lezama er at [Phys. Rev. A 61, 013801 (2000)] the ND
FWM spectra corresponding to different pump and probe polarization cases ar
e calculated and discussed. The calculated spectra are compared to the obse
rvation of NDFWM within the 6S(1/2)(F = F)-->6P(3/2)(F = 5) transition of c
esium in a phase conjugation experiment using magneto-optically cooled atom
s.