The equation of state of asymmetric nuclear matter is still controversial, as predictions at subsaturation as well as above-normal density diverge widely. We discuss in this lecture several experimental observables measured in heavy-ion collisions in the energy range 20-400 AMeV. Estimates of the density dependence of the symmetry energy are derived from comparison of experimental results with those of transport codes with different implementatiosn of the potential part of the symmetry energy, or in statistical model frameworks.