Seven markers of ascending (corticopetal) dopaminergic, noradrenergic and serotonergic neurones and choline acetyltransferase activity have been studied postmortem in frontal and temporal cortex from subjects with Alzheimer's disease and compared with a matched group of controls. Dopaminergic neurones (concentrations of dopamine, dihydroxyphenylacetic acid and homovanillic acid) were not deficient but some markers of the other neurones were affected. Noradrenaline and serotonin concentrations were reduced whereas the concentrations of their metabolites were either unaltered (5-hydroxyindoleacetic acid) or increased (3-methoxy-4-hydroxyphenylglycol). All deficits were most pronounced in the temporal cortex. Severely demented subjects had evidence of generalized neuronal loss, whereas those with moderate dementia showed significant loss of only choline acetyltransferase activity. In Alzheimer subjects, a significant relationship (inverse) was found between 5-hydroxyindoleacetic acid concentration and the number of neurofibrillary tangles.