Objective. Elevated levels of interleukin-8, a potent chemoattractant and activator of neutrophils, are associated with infectious and inflammatory diseases. However, little is known about interleukin-8 expression in human dental pulp. The purpose of this study was to determine whether tissue levels of interleukin-8 are elevated in irreversibly inflamed human pulps. Study design. Experimental samples were from teeth clinically diagnosed with irreversible pulpitis (diseased pulps). Controls were from freshly extracted, caries-free third molars (normal pulps). Samples were subjected to enzyme-linked immunosorbent assay and/or immunohistochemical analysis with specific antibodies to interleukin-8. Results. The enzyme-linked immunosorbent assay studies showed elevated levels of interleukin-8 in diseased pulps (mean, 1.82 ± 0.79 pg/mL/μg protein), as compared to detectable interleukin-8 levels in samples from normal pulps (mean, 0.08 ± 0.04 pg/mL/μg protein; P < .05). Immunohistochemical analyses demonstrated that diseased samples exhibited a higher density of localized interleukin-8 staining in areas with heavy infiltration of inflammatory cells. In contrast, normal pulps showed negative or weak interleukin-8 staining. Conclusions. Interleukin-8 concentration was higher in pulps diagnosed with irreversible pulpitis; only negligible amounts of interleukin-8 were present in normal pulps. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;88:214-20)