The present study investigated the 25% E rosette inhibition titer and vitamin A intake levels of patients with dysplastic or neoplastic lesions of the oral cavity as compared to control subjects with or without a variety of other oral diseases. All subjects were followed with repeat examinations beginning at the time of entry in the study and approximately every 6 months thereafter. E rosette inhibition titers generally increased as the lesions became more dysplastic. In the control group titers remained at a low level throughout the study. Vitamin A intake levels were mostly below one-half or above twice the recommended daily allowance in patients with dysplasias and in a few controls with nondysplastic oral disease. Some patients with dysplasias were in the normal range. The results of vitamin A measurements were compatible with a variety of studies suggesting a role for vitamin A in the genesis of epithelial dysplasias. The pattern of observed E rosette inhibition titers was in keeping with previous work in our laboratory as well with that of others who described a correlation between the height of titers and the degree of dysplasia.