OK, here's what I found out. Testing with a known HDR image that casts shadows... HDR images DO NOT produce raytraced light as a spot, distant or bulb light do. This seems to be an integral component in producing the shadow catching effect. I tested with both the standard distant bulb (which produces the shadow) and the by making that light invisible and using an HDR that seems to cast shadows. In the case of the HDR, the shadow-catcher showed up in the render... all of it, not just the shadow. So it seems that this, groucho, is a no-go for using that particular function. I may be able to find a workaround but this may take a bit. Somebody sound off if they've already found one! Thanks Ken