Determinations by spectrochemical analysis and flame photometer show that the ratios SrfBa and NafK both vary over a wide range in the alkali feldspars of the Langesundsfjord pegmatites, and that there is a pronounced positive correlation between these ratios. The variations are observed also within individual pegmatite bodies. On the average the feldspars appear to be richer in Sr than in Ba. Sr seems to substitute mainly forNa, as Ca is a minor constituent only. The origin and development of the pegmatite bodies is discussed. Minor constituents of some other pegmatite minerals are determined and briefly discussed. Nepheline occurring with Sr- and Ba-rich feldspar is extremely poor in these elements.