All patients had detectable levels of IL-18 mRNA in the uninvolved skin. Table 3 shows the range, mean ± SD and median levels of cytokine gene expression in each skin biopsy at the different times before and after receiving medication whether topical or systemic. Comparisons between median IL-18 expression levels with percentiles in all studied patients are presented in Figure 1 . Significantly lower IL-18 expression in uninvolved skin than lesional skin before treatment (P = 0.001) and lesional skin after treatment (P = 0.002) was observed in all studied patients as one group. The IL-18 expression in the psoriatic skin lesions after treatment was significantly lower than lesional skin before treatment (P = 0.023).