Second hallway, as with the first hallway don't hesitate to shoot to kill. Afterwards it's standard puzzle business push blocks to climb up stuff etc. You may have to kill the tube monster at the other side before you can jump.

Go back down and climb up the next ledge, here you'll have to do a running jump (hold directional button right then press up as you near the ledge) to get to the other side as the rail is broken. Ignore the healing serum guarded by the female zombie on the first floor, the game will provide you with ample healing stuff. Jump and climb up the first ledge you can (the one that leads to the tube monster that throws parasites at you right as you enter the room), kill everything you see and flip the switch guarded by the 'tube monster'. first puzzle room, broken railings can't be hung up to. first hallway, just keep shooting the zombie girls and parasites that jump at you, don't even turn around for the zombie guys who fall from the ceiling, distance if your friend. The only thing you can safely kick is the parasite monster, kick then stomp it right away (like you would the flies in stage one), only do this if you have a great sense of timing. Kicking things to death takes too much time so the horde of zombies will catch up to you that way. I killed all the monsters I encountered through the use of my pistol. I think the secret to stage three is that you shouldn't be afraid of wasting all your bullets.