Differences in the response of August rats' hippocampal field СА1 and СА3 neurons to the chronic haloperidol administration (a model of parkinsonism) were revealed by interferometric methods. Based on the morphochemical parameters (nuclear and cytoplasmic area, protein content and concentration), the changes of field СА1 neurons can be regarded as functionally active (all parameters are significantly higher than in controls), and those of field СА3 neurons - as initial stages of degeneration (the significant decrease of neuron sizes). The differences in the response found in this study can be associated with the functional characteristics of СА1 and СА3 fields.