Background: Recently, high efficacy of the chemotherapeutic regimen combining clarithromycin (CAM) with lenalidomide (Len) and dexamethasone (Dex) (BiRD) in treating multiple myeloma (MM) patients has been reported. However, the exact mechanism of added CAM has not been fully elucidated. This case report will provide helpful information for understanding the significance and the mechanism of action of CAM as an add-on therapy. Patient: A 78-year-old female patient with IgA-λ type MM was treated with low-dose Len coupled with low-dose Dex (low Rd), and excellent response was achieved for long term, but she later became refractory to this treatment. Then, CAM was added to low Rd (low Rd-CAM, i.e., modified BiRD therapy). This add-on-therapy was found to be effective, but later suspended because of pneumonitis. Then, low-dose Len coupled with CAM (low R-CAM) treatment was applied; but effect of this Dex-free treatment was insufficient. Thus, low Rd-CAM was reapplied and satisfactory reduction of IgA was achieved. This fact suggests that low Rd-CAM is the favorable combination, Dex is requisite and CAM might have enhanced the effect of Dex. In this case, various serum cytokines were examined during the course of illness. Only interleukin-6 showed apparent increase, and tumor necrosis factor-α, transforming growth factor-β, soluble IL-2 receptors and C-reactive protein showed the slight increase during low Rd-CAM treatment. The results seem somewhat conflicting, but it seems that intricate cytokine response due to immune activation might have occurred during low Rd-CAM treatment.