Pyroxene analyses of superior quality, from DSDP Legs 11, 15, 17, 34 and 37 have been studied statistically using cluster and factor analysis. These techniques are used to identify the various basalt groups using pyroxene chemistry, and to gain information about pyroxene crystal chemistry. The tholeiitic and alkalic pyroxene groups differ primarily in Cr2O3, TiO2, and Na2O contents. Relative to an average deep sea pyroxene, the tholeiitic pyroxenes are enriched in Cr2O3 and depleted in TiO2 and Na2O, while the alkalic pyroxenes are depleted in Cr2O3 and enriched in TiO2 and Na2O. The primary substitutional couples for the two groups are: VITi-IVAl2 and VIFe3¿-IVAl.