Magnetoresistance measurements on CeP have been performed between about 5 a
nd 40 K in magnetic fields up to 6 T. A complex phase diagram with six diff
erent phase transitions is derived. In particular, we find a second phase t
ransition in the supposed antiferromagnetic phase at zero-magnetic field. T
he magnetotransport behavior is discussed in relation to the magnetic struc
ture in each phase. [S0163-1829(99)05245-5].