mRNA species encoding B hordeins and B hordein protein have been localised in developing barley caryopses using in situ hybridisation and immunocytochemistry. B hordeins are first detected immunocytochemically in sections from 5 dpa (days post anthesis) barley caryopses. At this stage the endosperm is well differentiated and hordein levels are relatively constant across the starchy endosperm though notably absent from the aleurone layer. Analysis of serial transverse sections through later stages of caryopsis development (7-10 dpa) show a distinct differential accumulation of B hordeins. Hordeins accumulate at the periphery of the starchy endosperm, towards the apex and along the endosperm/scutellum boundary. Using in situ hybridisation B hordein mRNA was detected in equivalent patterns to the protein indicating that there is regulation of gene product accumulation at a transcriptional level. 3-D reconstruction of hordein in developing barley caryopses have been made using data from multiple serial sections in conjunction with a commercial computer-aided design package.