Hysteresis loss of swollen gum, filled natural rubber (NR), and styrene-butadiene rubber (SBR) vulcanizates have been determined from force-retraction measurement and dynamic mechanical analysis. The lowest value of hysteresis loss measured from force-retraction curve has been ob tained for vulcanizates swollen in xylene. Hysteresis loss is greater at 40% elongation than at 1% elongation for all the vulcanizates. The values obtained under dynamic conditions for swollen rubber vulcanizates show some anoma lous behaviour. Storage modulus (E') decreases both for NR and SBR vulcanizates on swelling. Samples swollen in xylene give the lowest value. As expected, E' values are higher at lower amplitudes. Loss modulus (E") in creases with loading of filler both for unswollen NR and SBR vulcanizates. On swelling of the vulcanizate, the loss modulus shows the same trend as above at high amplitude whereas low amplitude results illustrate the opposite trend. Loss tangent of the swollen vulcanizates shows the same anomalous behaviour as E" at low amplitude.