Using the Semantic Differential, the attitudes of thirty-five public librarians participating in a training program on library service to the inner city were measured before and after the conference. A group of thirty public librarians in similar positions in large cities was randomly selected and measured with the same instrument to serve as a basis of comparison and control. Three of the five concepts tested--Community Involvement in Planning Library Programs, The Urban Poor, and Library Institutes as Educational Devices, underwent statistically significant changes as a result of the five-day institute. Comparing the post-test scores of participants and the control group reveals that participants' opinions of four of the five issues moved in the opposite direction from the views of their colleagues. A discussion of two competing theories of why attitudes change in institute settings--interpersonal context versus ideational content follows, with hypotheses for testing their relative influence. (Author)