Ten human jejunal biopsy specimens were examined by both immunofluorescence (IF) and immunoperoxidase (IP) methods to compare both plasma cell counts and the distribution of extracellular immunoglobulins. Each specimen was cut into at least two portions, one fixed in 5% formaldehyde in phosphate-buffered saline before being snap-frozen and sectioned on a cryostat for IF, the other being fixed in half-strength Zenker and embedded in paraffin wax by standard methods for IP. Plasma cell counts were comparable in the eight biopsy specimens for which they could be estimated, geometric mean values being IgA 22.9 (IF), 19.3 (IP) and IgM 9.5 (IF), 10.6 (IP). Two specimens showing subtotal villous atrophy had too much extracellular IgA for plasma cell counts to be feasible. For these the IF methods had the advantage that the extracellular immunoglobulin was more readily distinguishable from background staining.