BACKGROUND Experimental sensitization depends upon the amount of allergen per unit skin area and is largely independent of the area size. OBJECTIVES This study aimed at testing if this also applies for elicitation of nickel allergy. PATIENTS/METHODS 20 nickel allergic individuals were tested with a patch test and a repeated open application test (ROAT). Nickel was applied on small and large areas. The varying parameters were area, total dose and dose per unit area. RESULTS In the patch test, at a low concentration [15 microg nickel (microg Ni)/cm(2)], there were significantly higher scores on the large area with the same dose per area as the small area. At higher concentrations of nickel, no significant differences were found. In the ROAT at low concentration (6.64 microg Ni/cm(2)), it was found that the latency period until a reaction appeared was significantly shorter on the large area compared to the small area. It was also found that the ROAT threshold (per application) was lower than the patch test threshold. CONCLUSION For elicitation of nickel allergy, the size of the exposed area and therefore the total amount of applied nickel, influence the elicitation reaction at some concentrations, even though the same dose per unit area is applied.