The chaotic hypothesis discussed in Gallavotti and Cohen (1995) is tes
ted experimentally in a simple conduction model. Besides a confirmatio
n of the hypothesis predictions the results suggest the validity of th
e hypothesis in the much wider context in which, as the forcing streng
th grows, the attractor ceases to be an Anosov system and becomes an A
xiom A attractor. A first text of the new predictions is also attempte
d.