All assay chemistries are subject to experimental error or interferences which can lead to false interpretation of data sets. Multiplexed combinations of compatible assays offer a convenient and cost-effective manner to address variation (by response normalization), flag non-conforming orthogonal data points and increase per well content. Although greatly informative, special attention should be paid to experimental design and the interpretation of multiplexed data sets due to the transient or kinetic nature of mechanistic biomarkers. Fig. (8) . Bioluminescent Protease Assay Signal. Stability Cyto-Tox-Glo™ Reagent was added to blends of experimentally lysed and untreated HL-60 cells. Luminescence was measured using a BMG Polarstar™ in kinetic mode for 3 hr.  Relapsing macrophage activating syndrome in a 15-year-old girl with Still's disease: a case report INTRODUCTION: Macrophage activating syndrome is a severe, potentially life-threatening condition that may accompany Still's disease. It is characterized by fever, hepatosplenomegaly, lymphadenopathy, severe cytopenia, serious liver dysfunction, coagulopathy and neurologic involvement. The principal treatment for patients with this syndrome includes etoposide 150 mg/2 M twice a week for two weeks, dexamethasone 10 mg/2 M for two weeks and cyclosporine 3 mg/kg to 5 mg/kg for a longer period. Cases of relapse of macrophage activating syndrome are relatively rare. CASE PRESENTATION: We describe the case of a 15-year-old Iraqi girl with Still's disease who developed macrophage activating syndrome with acute respiratory distress syndrome that required resuscitation and mechanical ventilation. Following intensive treatment, including high dose steroids and cyclosporine, the patient improved significantly. Two weeks after cyclosporine was discontinued, however, she was readmitted with an acute relapse of macrophage activating syndrome manifested by spiking fever, arthralgias, maculopapular rash and leukocytosis. This time the patient recovered following the reintroduction of treatment with cyclosporine and the addition of mycophenolate mofetil (Cellcept). CONCLUSION: We believe that cyclosporine is a cornerstone for the treatment of Still's disease. We recommend continuing this medication for several weeks following the patient's clinical recovery in order to prevent macrophage activating syndrome relapses. Macrophage activating syndrome (MAS) is a severe, potentially life-threatening condition that is characterized by fever, hepatosplenomegaly, lymphadenopathy, severe cytopenia, severe liver dysfunction, coagulopathy and neurological involvement [1] . The principal treatment for patients with this syndrome includes etoposide 150 mg/2 M twice a week for two weeks, dexamethasone 10 mg/2 M for two weeks and cyclosporine 3 mg/kg to 5 mg/kg for a longer period of time. Relapsing cases of MAS are rela-tively rare. However, there are several case reports that describe a relapse happening after a short treatment or after the dose of cyclosporine was decreased rapidly [1] .