This a theoretical Letter based on density functional theory, on the role of superoxide anion in firefly chemiluminescence in DMSO. We have found that this anion can attack luciferin radical molecules, thus forming a luciferin-like trianion. This latter molecule transfers an oxygen atom, which results in the formation of oxyluciferyl radical dianion and carbon dioxide molecules. Oxyluciferin is finally formed after an electron transfer from oxyluciferyl radical dianion to tert-BuO center dot radical molecules. Thus, we have found evidence that firefly oxyluciferin can be formed in a energetically favorable superoxide anion-assisted reaction, without the need for the formation of firefly dioxetanone. (C) 2013 Elsevier B. V. All rights reserved.