To further explore the influence of personality factors on response to phenothiazine treatment, we examined the relationship between the hospitalization proneness scale (HPS) and the effectiveness of phenothiazine treatment in delaying hospitalization for those patients hospitalized during the course of their clinic treatment. The 129 hospitalized patients were part of a larger cohort of 446 chronic schizophrenic outpatients randomly assigned to placebo, promazine, and chlorpromazine and treated under double blind conditions. The patients in this sample were hospitalized after from 1 to 114 months of continuous outpatient treatment. The patients were divided into hospitalization prone and nonprone groups on the basis of the HPS. The HPS consists of measures of the patients effectiveness in social interactions, cognitive performance, and social attainment assessed at intake. The findings indicate that the number of months the patient was able to remain in outpatient treatment prior to hospitalization is the result of an interaction between the specific drug received and level of HPS score (p< .01). A multiple range test indicated that among prone patients, those treated with either chlorpromazine or promazine remained in treatment for a significantly longer period of time than comparable placebo-treated patients (p< .05). On the other hand, nonprone patients treated with chlorpromazine were hospitalized after a significantly shorter period of time than nonprone patients treated with either placebo or promazine (p< .05). In addition, chlorpromazine-treated nonprone patients were hospitalized significantly earlier than chlorpromazine-treated prone patients (p < .01). The results were discussed in terms of the relationship between the personality attributes measured and the sedative characteristics of the drugs employed. The implications of the findings to drug treatment and future research were also discussed.