IQI/Jic (IQI) mice are an ICR-derived inbred strain developed in Japan, and it is known that aged females of this strain develop allergic dermatitis of spontaneous nature. In the present study, young IQI female mice which were sensitized with picryl chloride (PCL) to the shaved skin of abdomen and then topically applied with PCL to the ear at 4, 11, 18 and 25 days after the sensitization were examined. The ear swelling response increased rapidly after the 1st application, peaked after the 2nd one, and then gradually decreased. Histopathologically, edema with inflammatory cell infiltration developed after the 1st application and progressed after the 2nd one. The number of mast cells, CD4-positive cells and MHC class II-positive cells became prominent accompanied with epidermal thickening and dermal fibroplasia after the 4th application when clear elevation of total serum IgE levels was observed in many mice. Compared with the dermatitis induced in the same way in BALB/c female mice, the nature was similar with each other but the degree was obviously severer in IQI female mice. IQI female mice are considered to be a useful laboratory animal for the investigation of allergic dermatitis.