The keratinocytes from normal skin, uninvolved, and involved psoriasis were cultured in the presence of IL-6, IL-8, epidermal growth factor (EGF), hepatocyte growth factor (HGF), transforming growth factor-α (TGF-α) epiregulin, amphiregulin, and TNF-α and then MTT assay for keratinocytes proliferation was performed. This evidence concerns the gene EREG and psoriasis.