In order to investigate the mRNA expression and function of interleukin-23 (p19/p40) and interleukin-12 (p35/p40) in the psoriatic lesion, no-lesion and normal human skin, reverse transcriptase-polymerase chain reaction (RT-PCR) was used to detect the expression of IL-23 (p19/p40) and IL-12 (p35/p40). The results showed that the expression of IL-23p19 mRNA and p40 (IL-12/IL-23) mRNA were higher in psoriatic lesion than those of non-lesional skin and normal skin. The levels of IL-23p19 mRNA and p40 (IL-12/IL-23) mRNA were higher in psoriatic non-lesional skin than normal skin. However, no significant difference was found in the level of IL-12p35 mRNA among the psoriatic lesional skin, non-lesional skin and normal skin. It was suggested that IL-23 might be more important in the pathogenesis of psoriasis than IL-12.