Seventeen patients (six women and 11 men) with Jessner's lymphocytic infiltration of the skin were studied. Nineteen biopsy specimens were analyzed with the following monoclonal antibodies: UCHL1 (T cells), 4KB5, L26 (B cells), LN1 (germinal center B cells), and BerH2 (Ki-1⁺ cells). Routine direct immunofluorescence was performed on 15 specimens. In 10 of 19 specimens both B and T cells were demonstrated; the B cells were in close proximity to small blood vessels. In 50% of these cases the B cell component expressed LN1 positivity. We use the term perivascular lymphocytoma to describe this pattern. Nine specimens showed T cells only. No Ki-1⁺ cells were detected. Routine immunofluorescence studies were performed on 15 specimens. In six of seven specimens in which there was a mixed cell population of B and T cells, results were completely negative. In contrast, six of the remaining eight specimens with a predominantly T cell population revealed weak, patchy, granular, positive labeling for immunocomponents, particularly IgM and C3 at the basement membrane. These findings suggest that Jessner's lymphocytic infiltration is a heterogeneous disorder with at least two separate immunophenotypes. The finding of perivascular follicular center differentiation in more than half the specimens suggests a possible relationship in these cases to other benign lymphoid hyperplasias (pseudolymphomas).