Interleukin-8 (IL-8), a neutrophil chemoattractant, is a potent proinflammatory cytokine. This study showed that radicicol, an anti-fungal antibiotic, inhibited IL-8 gene expression, and IL-8 gene expression is mediated through activated mitogen-activated protein (MAP) kinase pathways. Radicicol suppressed IL-8 gene expression in PMA/LPS-stimulated THP-1 human monocyte cell line. The PD98059 and SB203580, known as a specific inhibitor of ERK and p38 kinase respectively, were used to find which pathway is more important for IL-8 gene expression. The RT-PCR data showed that radicicol and PD98059 inhibited IL-8 gene expression. SB203580 did not inhibit IL-8 gene expression as effectively as PD98059. NF-kB and AP-1 are critical transcription factors for IL-8 mRNA transcription, and their DNA bindings are also inhibited by radicicol, PD98059 and SB20350 as shown by gel retardation study. The other transcription factors, NF-IL6 and Octamer DNA binding activites were not affected by radicicol. In Western blot analysis revealed that phosphorylation of ERK1 was attenuated by radicicol. Radicicol showed weak inhibitory effect on phosphorylation of ERK2 and p38 MAP kinase. This study proposes that radicicol inhibits IL-8 gene expression in human monocytes.