Alkalic to subalkalic bimodal Tertiary igneous rocks from the Red Sea costal plain at Al Lith, Saudi Arabia, represent early rift volcanism in the central part of the Red Sea rift. Initial 143Nd/144Nd and 87Sr/86Sr plot within or near the enriched mid-ocean ridge basalt (MORB) field and show a variation in ϵ-Nd values from +4.1 to +7.7. The data are intermediate between more depleted basalts from the Red Sea spreading axis and less depleted alkalic basalts from the southeastern Arabian sheld and carbonatites from the East African rift. Pb isotopic compositions in alkali and tholeiitic basalts show a variation in 206Pb/204Pb from 18.0 to 18.9 and plot in and slight above the MORB envelope. Relatively low 206/Pb204Pb and variable 207Pb/204Pb and 208/204Pb in tholeiitic volcanics are compatible with a component from either old lithospheric mantle or lower crust containing ancient sediment. The isotopic compositions suggest mixing of asthenospheric and lithospheric sources but show no evidence for changing proportions of these components during early rift volcanism at Al Lith. Volcanism in the central part of the Red Sea is tholeiitic, consistent with a larger degree of melting or melting at increasingly shallower depths as rifting progresses. ¿ American Geophysical Union 1989