It is quite difficult to confirm the diagnosis of demential disorders, including senile dementia of the Alzheimer type (SDAT) by clinical means only. Through the combination of 99mTc-HMPAO brain SPECT and serum vitamin B12 determination it was hoped to speed up and improve the diagnosis of SDAT. 116 patients who had been divided into four groups according to their defect pattern in the 99mTc-HMPAO brain SPECT 17 very probably had SDAT; of these 15 showed a defect-pattern with brain SPECT which could be associated to SDAT. The majority of SDAT patients had serum vitamin B12 levels in the lower normal range or pathologically below that range. Both investigations contributed to establishing the SDAT diagnosis without replacing other investigations. The determination of serum vitamin B12 does not require any major additional effort.