The pro-inflammatory cytokine interleukin-1 (IL-1) is constitutively expressed by keratinocytes in vivo and has been shown to be expressed in psoriatic lesional skin. To determine what role the IL-1 system might contribute to the inflammatory process in psoriasis, semi-quantitative RT-PCR and cRNA microarray studies were performed on biopsies excised from lesional and non-lesional skin. Whilst IL-1α mRNA levels showed a reduction in lesional skin in a subset of patients, steady state IL-1β mRNA was increased markedly. Neither of the two IL-1 receptor transcripts nor total IL-1 receptor antagonist exhibited major changes within the lesion. Expression of the IL-1-induced chemokine IL-8 was only observed in lesional epidermis. Functional genomic experiments comparing transcriptome profiles derived from psoriatic lesional skin and IL-1 stimulated keratinocytes demonstrated a striking level of overlap. Taken together, these data suggest that IL-1 is likely to be an important mediator in the initiation and maintenance of psoriatic plaques and may represent an attractive therapeutic target.