Bruce,
We run a negative control for every patient's block requested.  For
example, if an S-100 and HMB-45 is requested on two blocks, you
would have a NEG control slide,  S-100 patient slide and HMB-45
patient slide for each block.  We would run a positive control for
the S-100 AB and HMB-45 AB.  (All total this would be 8 slides for
two blocks, two separate antibodies.)
Beth Morehead
Med U of SC