The following monoamine transmitters and related neurochemicals were analyzed in hippocampus and substantia innominata from postmortem brain tissue of subjects with senile dementia of the Alzheimer's type (SDAT): tryptophan (TP), 5-hydroxytryptamine (5-HT), 5-hydroxyindole-3-acetic acid (5-HIAA), noradrenaline (NA), dopamine (DA) and homovanillic acid (HVA). The results were compared to those obtained in postmortem brain samples obtained from normal subjects matched for age, sex and time between collection of tissue and freezing. There were no significant differences in concentrations of TP, DA or HVA between normals and SDAT subjects in either brain region. While hippocampal 5-HT, 5-HIAA and NA concentrations were markedly reduced in SDAT patients relative to normals, the substantia innominata concentrations of these three were not significantly different between controls and SDAT patients, emphasizing the importance of detailed regional analyses when conducting neurochemical studies in SDAT.