The aim of our study was to evaluate the prevalence of thimerosal allergy in subjects free of dermatitis. 256 recruits, selected by the Military Health Authorities as healthy subjects, without dermatitis or ocular defects, underwent allergological examination. The percentage of sensitization observed (6.25%) was compared to that found among 2150 patients, consecutively admitted to the Allergological Service of our Department, with suspected allergic dermatitis. Here we found 76 positivities (3.53%). Contact sensitization to ammoniated-mercury is lower among thimerosal-negative subjects (1.88%) than among both the healthy group of thimerosal-positive subjects (12.5%) and thimerosal-positive patients (11.84%). In the group of 76 positive patients it was not possible to relate the sensitization to thimerosal to either a particular clinical dermatological picture or to a specific exposure.