One-atmosphere synthetic systems, notably the system CaO-MgO-Al2O3-SiO2-Na2O (CMASN), have long been used in the study of alkaline rock petrogenesis. However, although much is known about phase relations, few studies provide quantitative data on liquid compositions. Systems that were considered previously, for example larnite-nepheline-forsterite-silica, were limited to compositions with high Na/Al ratios. Thus, some important end-members, like anorthite, could not be shown. This study fills a part of the gap between CMAS and the high Na/Al compositions of CMASN.In the composition range investigated, 7 phases have been encountered: liquid, forsterite, diopside, plagioclase, spinel, melilite and nepheline (liq, fo, di, pl, sp, mel and ne, respectively). The phase relations are such that 3 invariant points ([di], [sp], [ne]) are stable, and 3 ([fo], [pl], [mel]) are metastable. Twelve univariant (5-phase) assemblages are also present. Along with their divariant counterparts, they constitute most of the parageneses found in silica-undersaturated alkaline rocks.The liquidus equilibria in CMASN at 1 bar provide a very useful framework for discussing the petrogenetic problems of alkaline rocks, like the pl-mel incompatibility dilemma.