The secondary power stations on the National Grid, as distinct from the main base-load stations, are usually referred to as two-shift and one-shift stations. About 80% of the stations connected to the Grid belong to the last-mentioned categories.In this paper are discussed the status and function of these stations in relation to the Grid; some running and maintenance problems brought about by Grid operation; and some of the factors affecting cost of production. Overhead costs, which in the majority of stations have not been greatly affected by Grid operation, are not considered. It is shown that by the natural process of technical evolution the number and capacity of the secondary stations will gradually increase, and it is suggested that improvements in load factor and in the shape of the national load curve will not keep pace with technical station development to an extent sufficient to alter this tendency materially.The object of the paper is to draw attention to the less spectacular but important part played by these power stations, which have taken their place on the Grid as a result of the operation of natural laws. Efficient and economic operation of the secondary stations has undoubtedly contributed in no small measure to successful Grid operation, and, although many of these stations have suffered increased operating costs and lower thermal efficiency as a result of Grid operation, the supply industry has benefited as a whole.