A simple and precise means of measuring internal bond stresses in peel is now available. By the use of a newly designed “bond stress analyzer” the magnitude and positional distribution of internal normal stresses may be measured during peel. The design theory, construction, and operation of the instrument are reviewed in detail. The influence of the angle of peeling upon the cleavage stress distribution is investigated and analyzed. The results, interpreted in terms of present theory of peel adhesion, suggest that the peel test is a valid measure of interfacial adhesion properties only at a peel angle ofw=πrad=180 deg.The detailed form of the cleavage stress function in the region of boundary fracture indicates that cavitation and orientation processes contribute importantly to high peel strengths in elastomeric adhesive interlayers.