The electrophoretic transport of lambda-DNA in solutions of linear polyacrylamide (7 x 10(5) Da) has been investigated by electric birefringence. Three regimes depending on the concentration of polyacrylamide have been determined: at high concentration, a gellike regime shows a behavior that is compatible with reptation theory, and the birefringence signal shows the characteristic overshoot when the electric field is applied. At low concentration, the results are consistent with the formation of a 1-1 entangled complex of DNA and polyacrylamide. Between, a crossover regime is characterized by a threshold field above which the overshoot appears. It is shown that the threshold is correlated with the field where the lifetime of the entanglements of polyacrylamide becomes longer than the time of deformation of the DNA in the field.