Objective: To demonstrate the involvement of the root pulp in pulpitis, which may help in selecting a desirable therapy. Methods: Symptoms of 158 cases of caries-caused pulpitis were recorded and histologic diagnosis was made. The location of lesions was determined, and contributive rates and diagnostic indices were developed on the basis of the characteristics of various symptoms. Results: Computer analysis provided the following contributive rates in terms of symptoms: pain upon probing of the tooth (14.72%), duration of spontaneous pain of the diseased tooth (13.07%), intensified pain by cold stimulation (8.25%), and intensified pain by cold test during treatment (4.05%). The exact diagnostic rate was 76% on the basis of the above four contributive rates to demonstrate the involvement of the root of the tooth, while the dentist could only make a correct diagnosis 56.72% of the time. Conclusion: The four symptoms with the highest contributive rates improved the diagnostic rate of location, while other symptoms were excluded because of their uncertain contributive rates. As a result, the process of obtaining information was simplified. The tables of diagnostic indices are of value in clinical application as they are easy to learn and understand.