We compared the densities of lesions immunolabeled with ubiquitin, tau and beta A4 antibodies and stained by various silver impregnations, with the intellectual status. The densities of senile plaques and neurofibrillary tangles labelled by anti-ubiquitin antibody were correlated with the Blessed test score. Ubiquitin-positive neurofibrillary tangles were less numerous than those labelled by Gallyas, anti-tau, Bodian's and Bielschowsky's methods. There were five times more beta A4 deposits than ubiquitin positive plaques. beta A4 deposits could be numerous in cases in which ubiquitin immunolabelling was entirely negative. Bielschowsky's method, silver methenamine and thioflavin S revealed more senile plaques than anti-ubiquitin, whereas anti-tau, Gallyas', Bodian's and Cross' techniques revealed similar numbers. Anti-ubiquitin positive lesions were correlated with the severity of dementia. Compared with other staining methods, sensitivity of anti-ubiquitin was weaker for neurofibrillary tangles than for senile plaques. These findings suggest that ubiquitin epitopes are linked to the neurofibrillary changes (in the perikaryon or within the senile plaques), and are absent from beta A4 deposits, either diffuse or compact.