A partial study of the solid-solid equilibria in the quaternary system BaO-SrO-CaO-CuO has been undertaken in order to determine the observed phases and their evolution when Ba is substituted for Sr in mixtures (Sr/Ba)(2)CaCu2Ox and (Sr/Ba)(2)Ca2Cu3Ox. The temperature was fixed at 950 degrees C and samples were elaborated under 1 bar of flowing oxygen. It has been shown that two four-phased domains exist in this quanternary system, including the following phases : (Ba/Sr/Ca)CuO2, (Sr/Ca/Ba)(2)CuO3, (Sr/Ca/Ba)(14)Cu24Ox, and Ba4CaCu3O8 substituted Sr/Ca for the one and (Ba/Sr/Ca)CuO2, (Sr/Ca/Ba)(2)CuO3, (Sr/Ca/Ba)(14)Cu24Ox and (Sr/Ca/Ba)CuO2 for the other.