Ear skin responses to picryl chloride (PCL)-induced contact dermatitis were compared in detail between IQI/Jic mice developed in Japan and BALB/c mice often used for the investigation of contact dermatitis. PCL was applied to the left ear of each mouse 4 (1st), 11 (2nd), 18 (3rd) and 25 days (4th) after sensitization of the abdominal skin with PCL. Time course examinations were carried out on the ear swelling responses, total IgE levels, skin histology and immunohistochemistry for infiltrated cells after the 1st and 4th application. In IQI mice, the peak time of the ear swelling responses tended to shift from 24 h to 9 h with marked elevation of total IgE levels and marked increase of mast cells showing degranulation after the 4th application when CD8⁺ cells as well as CD4⁺ cells also prominently increased. In BALB/c mice, except for the total IgE levels and the number of mast cells, the degrees of ear swelling responses, histological changes and increase of CD4⁺ and CD8⁺ cells were much less severe. Female IQI mice are considered to be a useful mouse strain for further investigations on the role of CD4⁺ and CD8⁺ T cells in the pathogenesis of contact dermatitis.