Interleukin-1 (IL-1), originally defined as a product of activated macrophages, has since been found to be produced by many cell types including keratinocytes. The nature of this IL-1 activity in keratinocytes, originally known as epidermal cell-derived thymocyte activating factor (ETAF) has been the subject of many studies. In the course of this work it was found that the human keratinocyte cell line COLO 16 contains mRNA homologous to human monocyte-derived IL-1B. A 1.2 kbp cDNA was selected with a human IL-B probe from a lgt11 library constructed from COLO 16 mRNA. Sequence analysis revealed that this eDNA was nearly identical to the 3' 1.2 kb of human monocyte IL-1B. In addition, a partial cDNA (F8) was isolated from COLO 16 cells which has a distinct sequence from either IL-1a or B. There is evidence to suggest that the F8 message may be derived from differential splicing of a region of the human genome which also gives rise to the cGMP-gated ion channel in rod photoreceptor cells. The F8 cDNA hybridized on Northern blots of COLO 16 mRNA to a 1.6 kb message of low abundance. Antisera generated against a synthetic peptide based on inferred protein sequence from the cDNA reacted with a 20 and 30 kDa species in both COLO 16 cells and PMA-stimulated normal human keratinocytes. Expression of the partial cDNA in COS-1 cells resulted in activity in the thymocyte co-stimulation and D10.G4.1 T-cell stimulation assays, suggesting that ETAF activity may be due to a combination of IL-1 and F8. / Thesis / Master of Science (MS)