I think that there's a setting for the layer's opacity in layer properties/render settings. According to the Max help files:
Visibility—Controls the rendered visibility of the object. At 1.0, the object is fully visible. At 0.0, the object is completely invisible when rendered. Default=1.0.
Here's the full rundown on layers:
http://www.3dmax-tutorials.com/Layer_Properties.html
Joe Bourke
Owner/Creative Director
Bourke Media
http://www.bourkemedia.com