Summary A pull-out technique suitable for determining the interfacial bond strength for various combinations of fibres and matrix is described. In this method, a thick fibre, 0·5 to 1·0 mm in diameter, is embedded perpendicularly through a matrix material contained in a special mould and is stressed on a tensile testing machine. The value of the maximum bond load corresponds to a sharp break in the load-extension curve. Results show that the bond strength between E-glass-fibre and cement is of the same order as that between steel and cement but higher than the values reported for asbestos and cement. The work has also shown that the strength of the bond between E-glass-fibre and gypsum plaster is of similar magnitude, but that it is affected significantly by variations in water/plaster ratio.