Reported is a description of a system developed for diagnosing the epistemological characteristics of secondary school science teaching. Lessons were analyzed to determine whether they were epistemologically consistent with science. If not, changes were prescribed which could make the information consistent with science. The "Profile and Epistemological Analysis Scheme" (PREPISTAN scheme), the diagnostic instrument, contains three epistemological dimensions and a hierarchy of four categories of science statements. A fifth category, Sense Experience of State-Of-Affairs, is used to code opportunities pupils have to observe phenomena or to recall previous empirical experiences. Category codes of statements are used to generate lesson "profiles" of kinds of statements or observational opportunities over time to show the kinds of science statements and observation opportunities provided in science lessons and the relationships among categories occurring in sequence as part of an argument for verification of a statement. (Author/EB)