Cucumber cotyledons provide an excellent experimental system in which to investigate developmental changes in gene expression, from the early phase of heterotrophism through phototrophic growth to senescence. A cDNA library was prepared from the final stage of senescing cucumber cotyledons (> 95% yellow) for studying the genes responsible for lipid mobilization during germination and senescence. This library had produced numerous senescence-associated clones in a previous study. Here, a total of 365 cDNA clones and their expression levels were examined via semi-quantitative RT-PCR. Up-regulation of expression was detected for several known and unknown genes. These results were used to investigate the possible functions for senescence-related genes during cotyledon development.