Abnormalities in muscle histology have been reported frequently for the cricopharyngeus muscle of patients with oculopharyngeal muscular dystrophy, motor neuron disease and other neurological disorders in which dysphagia is a common clinical sign. However, there are few detailed reports of the normal structure of this muscle nor quantitative baseline data with which to compare the diseased state. In this study, cricopharyngeus muscles from 21 healthy individuals and four patients with motor neuron disease underwent quantitative histological and histochemical examination. In addition to the extensive connective tissue content (40%), comprising abundant elastic fibres, cricopharyngeus muscles from normal individuals possessed small calibre striated muscle fibres (mean narrow diameter 30 microns) of widely varying size (coefficient of variation 41%). The majority of fibres were histochemically type I (82%) and highly oxidative. All muscles comprised numerous muscle fibres with aberrant histological and histochemical features (internalized nuclei, 'ragged red' crescents, splits, degenerating fibres, 'moth-eaten' fibres, or nemaline rods.) The histomorphometric and histopathological features were similar in males and females and some showed a correlation with age. There were increases in fibre size and roundedness and decreases in the numerical density and percentage of type I and split fibres in the specimens from older individuals. Cricopharyngeus muscles from patients with motor neuron disease were not significantly different from the controls for most parameters. It is therefore suggested that previous descriptions of specific cricopharyngeal pathology accompanying neuromuscular disease or dysphagia be interpreted with caution. The importance of obtaining normal structural, morphometric and histopathological data from muscles other than the usually biopsied limb muscles, is emphasized.