The effectiveness of long-term retardants used in forest fire fighting has been studied at three different scales. In this paper, retardant effectiveness experiments conducted since 1965 are examined and reviewed. These experiments include studies carried out with analytical instrumentation as well as studies involving laboratory and field flame-spread tests. Special attention is paid to the work performed with diammonium phosphate (DAP) and ammonium sulfate (AS). The experimental methodologies and the results obtained are reviewed in detail. A lack of effort in the modeling of fire behavior under the effect of these products is evidenced and recommendations for further work are made. (C) 2008 Elsevier Ltd. All rights reserved.