We present mechanical measurements of the frequency-dependent linear viscoelastic storage and loss moduli, G＇(omega) and G "(omega), for calf thymus DNA (13 kbp) in a saline buffer over a range of mitotically relevant mass concentrations from C = 1 to 10 mg/mL. For C exceeding a critical entanglement concentration, C-e, we observe a dominant plateau elasticity, G＇(p), for large omega. As omega decreases, G＇ falls until it is equal to G " at the crossover frequency, omega(c), below which G " dominates. These measurements are consistent with a model of entangled semiflexible polymer coils in a good solvent, which predicts G＇(p) similar to C-2.3 and omega(c) similar to C-2.4.