Under pathological conditions, microglial cells undergo activation, which is manifested by the expression of histocompatibility locus antigens class II (HLA II) on their surface as well as by proliferation and varied morphological forms. In schizophrenia, characterised by an essential role played by immunological mechanisms, quantitative analysis of activated microglia -- with well-developed ramification (RM), degenerative traits and damaged processes (from their shortening to their complete lack) (DM) -- may contribute to better understanding of schizophrenia etiopathogenesis. Quantitative analysis was performed on slices derived from the frontal and temporal lobes of 9 brains of schizophrenics and 6 control brains. The nonparametric Mann-Whitney U test was used to assess quantitative differences in the distribution of microglia in these regions of the brain. Statistical analyses were performed with STATISTICA 6.5 Programme. In both structures of the brain, the number of activated microglial cells was higher in schizophrenic brains than in control brains. Except for the first layer of the cerebral cortex with the same amounts of RM and DM, the number of DM cells in the remaining regions was several-fold higher than that of RM cells. It is most likely that disturbances in calcium metabolism and energetic balance as well as antibodies produced in the course of schizophrenia are the agents able to trigger a cascade transforming RM into DM. Quantitative differences in RM and DM, observed between the studied structures and cortical regions, could depend not only on functioning of inter-neuronal and inter-structural links. Our study suggests a pivotal role of microglial cells in repair processes and/or etiopathogenesis of schizophrenia and indicates that they undergo substantial damage in the course of chronic schizophrenia.