Autonomic nerves in jejunal mucosa of HIV-infected patients show severe structural damage on electron microscopic examination. The aim of this study was to quantify loss of autonomic axons from the lamina propria of HIV-infected patients in different clinical stages of disease. Jejunal biopsies were taken from 19 HIV-antibody-positive homosexual men and from 10 control patients. Autonomic fibres in the mucosa were stained with a neurone-specific polyclonal antibody, PGP 9.5. The density of axons was quantified by a point-counting technique using a Lennox eyepiece graticule under light microscopic examination. There was significant reduction in axonal density in the villi of HIV-infected patients [mean, 9.0; standard deviation (s.d.), 4.7] compared with controls (mean, 15.3; s.d., 5.2; P = 0.003), and in the pericryptal lamina propria of HIV-infected patients (mean, 17.8; s.d., 5.4) compared with controls (mean, 27.3; s.d., 6.2; P = 0.0002). Although autonomic denervation occurs throughout the jejunal mucosa of HIV-infected patients, there was no correlation between the clinical stage of HIV disease and the degree of denervation. The denervation was greatest in patients with the most severe diarrhoea, but this difference was not significant. This study provides the first quantitative morphological evidence for depletion of autonomic nerves in the jejunum of patients infected with HIV. Autonomic neuropathy may contribute to chronic diarrhoea in HIV disease.