Since melatonin inhibits the growth of C6 cells, and this indoleamine has been demonstrated to be able to decrease aromatase expression and activity in other tumour cell lines, our objective in the present study was to analyse the possible effects of melatonin on the local synthesis of oestrogens in C6 glioma cells and its influence on the cell proliferation. This evidence concerns the gene CYP19A1 and neoplasm.