  We investigated the effect of high pressure on the field dependences of
magnetoresistance (MR) in La_{0.8}Ag_{0.1}MnO_{3} near the metal-insulator
transition temperature. Our results showed that an increase in pressure results
in a decrease in the magnitude of negative MR. At pressures $P\geqslant5.6$ GPa
and magnetic fields up to 4 kOe, we observed a positive MR. However, with a
further increase in magnetic field (>4 kOe), the MR again became negative.
Therefore, we discovered a "negative-positive" MR crossover induced by high
pressure near the transition temperature. We supported our experimental
findings with a qualitative theoretical interpretation using the electron-hole
model of MR. This theory explains observed the MR sign change.
