Cell-mediated immunity in rheumatoid arthritis (RA) was assessed by skin testing with 5 common antigens in 84 patients, dinitrochlorobenzene (DNCB) application in 13, and in Vitro phytohemagglutinin (PHA) stimulation of buffy coat cells in 39. Routine skin-test reactions were recorded as the largest diameter of induration present at 48 hours. Controls included normal subjects, family members of patients with rheumatic disorders, and patients with unrelated illnesses. Results revealed two populations of RA patients. Forty-two percent were completely anergic to the 5 antigens and 14% gave a history of herpes zoster. The remainder showed reactivity similar t o that seen in patient controls. Most RA subjects demonstrated normal or only minimally diminished PHA responses. The RA patients had normal inflammatory responses to the initial DNCB application, but immune reactions t o this agent paralleled skin-test reactivity t o the other antigens. The anergic individuals could be separated from the reactive population primarily by the increased duration of disease activity but not by medication taken or the degree of disease activity when tested.In rheumatoid arthritis (RA) the status of skin-test responsiveness and lymphocyte reactivity to phytohemagglutin (PHA) is in question. In some studies patients with kerato-