The problem of oxygen influence on the triplet quenching and photobleaching of a single dye molecule embedded in a polymer matrix was investigated. Indocarbocyanine in polymethylmetacrylate was used as a model system. A well-chosen amount of oxygen in the gaseous environment above the sample was shown to efficiently improve the conditions for the single molecule detection. Experiments on molecular ensembles suggest this amount to be close to 2% of oxygen in an otherwise inert atmosphere. (c) 2005 Elsevier B.V. All rights reserved.