IT has been reported by Carp, Licursi, Merz and Merz1,2 that the percentage of circulating polymorphonuclear neutrophils (PMN) in C57Bl mice was reduced permanently following injection with either multiple sclerosis or scrapie tissues. They reported that the decrease was first detected 3 d after injection in the case of scrapie and that the decrease persisted throughout the preclinical phase of the disease: most of their results were from mice bled 6 weeks after injection. We report here the confirmation of some of their findings and also discuss certain difficulties which can arise with this test.