For the purpose of assessing the involvement of L-selectin in atopic diseases, we measured L-selectin expressed on peripheral monocytes and serum soluble L-selectin (sL-selectin). We enrolled 7 patients with atopic bronchial asthma(BA), 6 patients with atopic dermatitis, 12 patients with Japanese cedar pollinosis(P), and 9 healthy controls(C). L-selectin expressed on peripheral monocytes was detected and analyzed by using flow cytometry. Serum sL-selectin was measured by enzyme-linked immunosorbent assay. Compared with the group C (81.7 on average), mean fluorescence intensity of CD 62 L on monocytes in the group BA was significantly higher (110.4 on average, p < 0.05). The group AD also showed higher tendency (101.3 on average, p < 0.08). No significant difference was found in serum sL-selectin levels among the four groups(BA: 1086 ng/mL, AD: 1226 ng/mL, P: 945 ng/mL, C: 1052 ng/mL, on average). There was a negative correlation (r = -0.69) between serum sL-selectin and age in all subjects (BA + AD + P + C). The results suggest that L-selectin is involved in the extravasation of monocytes toward local inflammatory sites in atopic diseases. Serum sL-selectin seems to stay at normal level in mild and stable atopic diseases, while the trend of high serum sL-selectin level in children may participate in the pathogenesis.