A method was developed for determination of interfacial toughness parameters from a new transverse single-fibre test. In previous work, experimental procedures were developed. Interfacial debond growth in the are and fibre direction was measured for transparent matrix polymer composites. In the present study, an earlier stress analysis by Toya was modified and combined with a critical energy release rate criterion, taking mode mixity effects into account. The developed model was used to determine interfacial toughness parameters. The model was able to describe and explain the main experimental observations of the debonding process. Treatment of the contact problem present for large debond angles is of interest for future work. (C) 1997 Elsevier Science Limited.