There has been a recognized need to understand the basis of quality teaching at the secondary school level. The Questionnaire on Teacher Interaction (QTI) was developed by T. Wubbels, H. A. Creton, and H. P. Hooymayers in the 1980s to address teaching quality at the high school level. A modified version of the QTI, the Professor Interpersonal Teaching Behavior Inventory (PITBI) has been developed to study college student perceptions. A reliability and validity study of the PITBI was conducted. Participants were graduate students in a university's college of education. Factor analysis revealed that 40 of the original 64 items were not relevant to the professor's interpersonal teaching behavior, an expected result because the original instrument was developed for high school students. Retained items factored into five factors, and these factored to one factor identified as Interpersonal Communication Teaching Behavior. Correlational relationships between retained items and the relationships among items were identified. The construct validity of the PITBI is predicated on that of the QTI. Validity was best for the leadership and guidance subscale, and good for the helpfulness, and uncertainty subscales, but not valid for the temperament subscale. It is recommended that additional items be added to the subscales other than leadership and guidance to strengthen their reliability coefficients. The validity of the instrument is based on the validity of its subscales. (Contains 31 references.) (SLD)