The techniques used for the production and identification of plant hormone mutants are described. The properties used to classify these mutants into the broad synthesis and response categories are discussed, and the genetic considerations needed to allow their effective use in plant hormone research examined. A brief outline of significant work on gibberellin (GA), abscisic acid (ABA), auxin, ethylene, cytokinin and phytochrome mutants is provided. The molecular action of these genes is discussed where available and recent rapid advances made in Arabidopsis highlighted. Suggestions for future emphasis are made, particularly relating to an examination of the tissue and ontogenetic specificity of the plant hormone genes.