Members of the MADS-box gene family control reproductive development in higher plants. In cucumber, floral development exhibits several interesting features related to a genetically determined sex-expression mechanism, that affects the differentiation of male and female flowers. In this study, three cDNA homologues of the homeotic gene AGAMOUS have been cloned from early-stage floral buds of Cucumis sativus and fully sequenced. Their expression was studied by Northern analysis using two contrasting sex genotypes, an androecious line and a gynoecious one. The three genes are expressed at low levels at earlier bud stages, the levels rising as the bud matures. Two of the clones, CAG1 and CAG3, are expressed in the third and fourth whorl of mature flowers, while CAG2 is restricted to the carpel; none is expressed in leaves. The transcript levels do not appear to be modulated by gibberellin or ethephon, two treatments that alter sex expression in cucumber. While MADS-box genes probably play an essential role in cucumber floral development, as they do in other plants, our findings may imply that the pathway leading to reproductive organ arrest in cucumber unisexual buds acts independently of MADS-box gene expression.