The effect of chronic imipramine (IMI) or electroconvulsive shock (ECS) treatment on the expression of group Ia metabotropic glutamate receptors (mGluR1a) was studied in the rat hippocampus by an immunohistochemical method, using a specific monoclonal antibody. It was found that both those treatments increased the number of mGluR1a immunoreactive neurons in a pyramidal layer of the CA3 hippocampal field. Moreover, IMI, but not ECS, increased the density of mGluR1 a positive neurons in the hilus. The obtained results indicate a possible influence of the antidepressive treatment on the mGluR1a expression in some hippocampal fields.