A selected set of precise measurements of the mean kinetic energy of f
ission fragments has been used for testing nuclear dissipation. Calcul
ations of the kinetic energy release on the descent from saddle to sci
ssion have been done with a dynamical model based on the classical Ray
leigh-Lagrange equations of motion. Both alternative dissipation mecha
nisms, one-body dissipation and two-body viscosity have been tested. A
n increasing strength of the dissipation with increasing mass of a com
posite system has been observed. However this effect may partly result
from a specific shape parametrization used in the dynamical model.