Elastic band mobilisation of repaired flexor tendons in zone 2 may be complicated by flexion contracture of the P.I.P. joint. The mechanics of three types of elastic band mobilisation were analysed from lateral video-recordings of finger movement and the flexion moment at the P.I.P. joint was derived at every 10 degrees of flexion. The conventional forearm attachment of the elastic band produced a steep rise in P.I.P. joint flexion moment during extension; this effect was greatest when the M.P. joint was at 70 degrees and least at 20 degrees. Flexion moments for attachments around the dorsum of the hand or under a palmar pulley were lower, uniform throughout the range of P.I.P. joint motion and independent of the position of the M.P. joint. The effort needed to extend the P.I.P. joint is strongly influenced by the method of elastic band attachment; consideration should be given to both tension and moment arm in application of elastic band mobilisation.