The central part of bacteriophage T4 baseplate is built of several proteins which are present in only a few copies per phage particle. Only some of these minor baseplate components have been identified previously as distinct protein species by biochemical analysis. We have used the bacteriophage T7 RNA polymerase expression system to identify and overexpress the minor baseplate proteins. The products of genes 25, 26 and 51 were identified on the autoradiographs after selective labelling with [35]S methionine. The overexpression of gene 25 and 51 products was high enough to make possible undertaking their purification and studies of their properties.