Cell adhesion molecules (CAMs) are known to play an important role in cell-mediated immunity and inflammation. To investigate the importance of one of the CAMs, lymphocyte function-associated antigen-1 (LFA-1) in allergic contact dermatitis (ACD), a specific anti-LFA-1 monoclonal antibody was injected into the ears of mice after sensitization but prior to challenge with dinitrofluorobenzene (DNFB). BALB/c mice were sensitized on the dorsal skin with DNFB, and challenged on the ears 6 days later. The effect of the antibody on the elicitation phase of contact sensitization was determined by its intradermal injection into the pinnae of the mice at doses of 1–40μg. At 24 and 48 h after challenge, ear swelling was dose-dependently suppressed by injection of LFA-1 antibody at doses of 2–40 μg, which are less than 10% of the systemic dose required for effective suppression of delayed- type hypersensitivity in previous studies. Maximal inhibition of ear swelling (44%) was observed after injection of 20 μg of anti-LFA-1 antibody. Inhibition of ear swelling was accompanied by a reduction in dermal oedema and leucocyte infiltration into the dermis. Our results suggest that LFA-1 plays a significant role in the elicitation of ACD reactions, and also that our test system is a sensitive and useful means of evaluating the blocking effect of antibody to adhesion molecules thought to be involved in the elicitation phase of ACD.