The formation of pollen from vegetative tissue passes through different phases: meiosis, development of the generative cell and vegetative nucleus, and synthesis of the pollen-wall and other pollenspecific compounds that have a function during germination and fertilization. The production of these pollen-specific structures and compounds is caused by changes in the gene expression of the plant and are concomitant with a series of processes by which type-specific gene products, e.g. mRNA’s, are formed. Analysis of the mRNA population in mature pollen from maize showed that 10% of this population represented pollen-specific mRNAs.