To clarify the immunologic abnormalities in patients with atopic dermatitis (AD), the percentages of Leu7 (HNK-1)-positive cells and natural killer (NK) cell activity were measured in peripheral blood lymphocytes isolated from 25 AD patients (8 males and 17 females, mean age of 20.8 years old) and 69 healthy non-atopic persons (46 males and 23 females, mean age of 27.4 years old). The percentage of Leu7-positive cells was significantly reduced in AD patients compared with that in controls (AD patients: 11.6 +/- 7.0%, controls: 19.5 +/- 8.3%, p less than 0.01). Although the difference was not statistically significant, reduction of the percentage was slighter in patients with mild AD than in moderate and severe AD patients (mild AD: 14.3 +/- 6.6%, moderate AD: 10.1 +/- 4.4%, severe AD: 10.5 +/- 8.3%). There was also a significant inverse correlation between the percentage of Leu7-positive cells and log IgE levels in patients with AD (r = -0.537, p less than 0.01). No differences in NK cells activity or NK cell activities augmented by interferon-beta and interleukin-2 were observed between in AD patients and in controls. These results suggest that the Leu7-positive cells in AD patients may be closely associated with the regulation of serum IgE production.