  We measure the penetration depth of optimally doped and underdoped
La2-xCexCuO4 in the millimeter frequency domain (4 - 7 cm-1) and for
temperatures 2 K < T < 300 K. The penetration depth as function of temperature
reveals significant changes on electron doping. It shows quadratic temperature
dependence in underdoped samples, but increases almost exponentially at optimal
doping. Significant changes in the gap anisotropy (or even in the gap symmetry)
may account for this transition.
