  We derive a posteriori error estimates in the
$L_\infty((0,T];L_\infty(\Omega))$ norm for approximations of solutions to
linear para bolic equations. Using the elliptic reconstruction technique
introduced by Makridakis and Nochetto and heat kernel estimates for linear
parabolic pr oblems, we first prove a posteriori bounds in the maximum norm for
semidiscrete finite element approximations. We then establish a posteriori
bounds for a fully discrete backward Euler finite element approximation. The
elliptic reconstruction technique greatly simplifies our development by allow\
ing the straightforward combination of heat kernel estimates with existing
elliptic maximum norm error estimators.
