In vitro effects of imipramine (IMI) and desipramine (DMI) at the doses of 10, 50 and 200 μg/mg protein on ATPases and ChE activities of human fetal brain were studied in the cell-free extract of cerebrum and cerebellum in different gestational ages, viz. 12-30 weeks. Both ATPases and ChE were found to be inhibited by IMI in a dose-dependent way, but DMI was almost ineffective. The inhibitions of ATPases and ChE by IMI in different sub-cellular fractions were characterized by the Lineweaver and Burk plot. Use of DMI in combination with diazepam (DZ) reveals that DMI can antagonize the DZ induced changes of ATPases and ChE enzyme system. DZ induced changes of these enzymes remain unaltered or potentiated when IMI is used with DZ.