I am using ArcMap 10.1 and I would like to remove all transparency from all the layers in the map at once.
Working off the answer given by Dan, this script will remove the transparency from all layers if you run it in the python window in arcmap.
mxd = arcpy.mapping.MapDocument ("CURRENT") df = arcpy.mapping.ListDataFrames (mxd, "Layers")  for lyr in arcpy.mapping.ListLayers (mxd,"", df): lyr.transparency = 0 arcpy.RefreshActiveView() mxd.save del mxd
Loop through your layers and use
arcpy.mapping and set the transparency property.