Helgeland, S. M., Nsess, R. R.&Grov, A. Delayed hypersensitivity to staphylococcal protein A detected by leucocyte migration inhibition. Acta path, microbiol. scand. Sect. C,83:15–18, 1975.Delayed hypersensitivity to staphylococcal protein A was indicated by the migration inhibition reaction (MIR), using peritoneal cells from protein A sensitized guinea pigs. No cross‐reactivity between protein A, polysaccharide A and peptidoglycan was found. Peptidoglycan fromStaphylococcus aureusstrain Cowan 1 inhibited almost completely the migration of cells from both sensitized and unsensitized ce