The temperature and stress dependence of creep of human digital tendon was studied in vitro at temperatures between 10 and 60°C and at tensile strains below 2%. The activation energy, ΔH, for the viscoelastic deformation mechanism was determined by imposing small, abrupt changes in temperature on the specimen during creep. The value of ΔH at 28°C was 12 (±1·5) kcal mol−1 for specimens from donors of age 21, 55 and 89 yr. The activation energy for the shrinkage transition in human digital tendon was determined as 250 kcal/mole using similar techniques. The stress dependence of the isochronal strain rate is roughly of the form ε α δn, n being less than unity. The observed viscoelastic phenomena are discussed in terms of the structure of the collagenous tissue. The advantages of the creep T-jump technique for the study of biological polymers are also discussed.