The criteria for monitoring tissue health around endosseous implants remain subjective. Disagreement about which clinical measures of peri-implant health are of diagnostic value continues because of the complexity of the disease process and lack of validated measures of peri-implant health. Crevicular fluid analysis of various inflammatory mediators has been investigated as a means of providing objective criteria of tissue health. In this clinical report, the crevicular fluid levels of interleukin-1 beta (IL-1 beta), an inflammatory cytokine, were used to provide an objective measure of the peri-implant health and the effectiveness of treatment for a patient with two failing implants. The measurement of IL-1 beta may be an important supplement to clinical findings in establishing a diagnosis of peri-implantitis.