In order to study the effects of advanced periodontitis on pulps, 36 human teeth were examined histologically. In addition, a medical and dental history was elicited. The pulps were intact, uninflammed in only 9 teeth (25%) of 36 periodontally involved teeth. 27 teeth (75%) had pulps exhibiting inflammatory lesions of varing intensities. Of 27 teeth with pathological pulp tissue alterations, focal reversible pulpitis was found in 4 teeth, chronic pulpitis in 13 teeth, pulp abscess in 6 teeth, and pulp necrosis in 4 teeth. These observations appeared to indicate that teeth with dvanced periodontitis produce a high incidence of degenertion and inflammation of the pulp. Responses to electric pulp test were not found to be reliable indicators of the state of the pulp in periodontally involved teeth.