This review summarises information on hydroxyproline-rich glycoproteins (HRGPs) and clones encoding these molecules isolated from male and female tissues of flowering plants. HRGPs are abundant in sexual tissues and a number of different HRGPs have been isolated. The protein and carbohydrate components of these HRGPs have been characterised and cDNAs encoding the protein backbones of several have been isolated and sequenced. Further work is directed at detailed structural analysis of the carbohydrate side chains of these molecules and their points of linkage to the protein backbones. The biological functions of most of these molecules have not yet been established unequivocally.