Previous studies using in vitro systems with various stimuli have shown that PBMC from patients with AD show increased levels of IL-4 but decreased levels of interferon-gamma (IFN-gamma) compared with PBMC from normal controls. However, in vitro conditions do not always mimic the in vivo condition. We therefore believe that it is important to quantify the expression of these cytokines in freshly isolated PBMC. This study examines the expression of IFN-gamma, IL-4 and IL- 13 mRNA in freshly isolated PBMC from adult patients with AD, from patients with psoriasis vulgaris and from healthy adults, using the semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method. Levels of IFN-gamma mRNA were significantly lower in PBMC of patients with AD than in controls. IL-4 mRNA levels did not differ significantly between groups. Conversely, levels of mRNA for IL-13 were significantly greater in PBMC of patients with AD than in controls. An increase in IL-13 expression may regulate the in vivo synthesis of IgE in patients with AD.