PIX Question...

Hi,
i have configured a Cisco Pix with 3 ethernet interfaces:

inside 192.168.10.1
dmz 192.168.15.1
outside x.x.x.x (public ip address)
it's ok!

inside have security-level = 100, dmz = 50 and outside = 0 so i can view the home page of my web server on the dmz (192.168.15.5)
from outside by means of NAT and an access-list in interface outside, and i can view it from inside too (by means of security level)....but why the ping from inside to dmz don't respond? why i can view the web server from from my lan to 192.168.15.5 but i can't ping it? or it can't respond me?
In the inside and dmz interface i don't have any access-list, it's a good idea to make an access-list for this interfaces?
Thanks and compliments for the web site :
Gippoz