Summary The paper discusses tests on 12 concrete beams prestressed by fibre-glass cords. The values of the forces in the cables are calculated on the basis of the test results. The influence of bond between tendons and concrete on the behaviour of beams is investigated. The low value of modulus of elasticity offibre-glass tendons is discussed. The results obtained on beams with fibre-glass reinforcement are compared with the results obtained on 23 similar beams prestressed with steel wires.