A patient under Taxol and granulocyte colony stimulating factor (G-CSF, Neupogen) treatment for metastatic breast carcinoma of the liver experienced repeated suicidal depression on days 10 and 11 of therapy. MRI and MRS were performed during the fifth and sixth cycles of chemotherapy on days 1 and 10. The MRI was normal in all four examinations. The MRS showed normal levels of metabolites on days 1 of therapy, with remarkable reproducible declines in neurobiochemicals myo-inositol (23-27%), choline (20-24%), creatine (10-14%) and glutamate/glutamine (22-39%) on day 10 of therapy. The neurobiochemical declines coincided with the patient's experience of suicidal depression. Patients reporting depression during standard cancer therapy may be experiencing previously undocumented chemotherapeutic neurobiochemical imbalances or neurotoxicity.