We have studied the effects of agar and agarose on Vent(TM) DNA polymerase and Tag DNA polymerase. Agar strongly inhibited Vent(TM) DNA polymerase but only moderately inhibited Tag DNA polymerase. Such a difference may be due to the fact that the two polymerases belong to different structural families. When Vent(TM) DNA polymerase is used to amplify DNA from lambda plaques, agarose rather than agar is the solid medium of choice.