The chemical content knowledge of secondary science teachers is seldom measured directly in developed countries as there are practical, ethical and political problems involved that would be likely to be insuperable. In Papua New Guinea (PNG), the author assisted in some of the work involved in the second IEA Science Study (SISS), where the PNG education system took part in the scheme which involved twenty-six different countries. The author suggested that the science teachers taking the classes being tested completed the tests themselves. These scripts were returned to be marked in the same way of the student scripts. The results of the research were significant and can be considered as a start to the fuller and more detailed research which would be necessary to be more confident of the conclusions. However, evidence was produced to indicate that that the knowledge of some experienced science teachers was less than would be considered desirable. The scientific knowledge Goroka diploma holders, whether experienced or more recent, was less as a group than other Grade 10 teachers. There was also evidence that chemistry is an area of difficulty, particularly for Goroka diploma holders. Item analysis of SISS data yielded some inkling of specific problems which national teachers had in their own understanding; it might eventually lead to appropriate solutions being found for these problems. Three appendices include: (1) International Science Study; (2) S.I.S.S. Tests data; and (3) Tests in the Separate Sciences data. (Contains 5 tables.) [This article has been published as: Palmer, W. P. (1986). The chemical knowledge of secondary science teachers in Papua New Guinea "Chemistry in the Service of Papua New Guinea," P. Bladon (editor), (12th-14th September), pp.167-190.]