Although production of noble gases in meteorites are well studied for many years, [e.g., Bogard and Cressy, 1973> the first analysis of cosmic ray produced helium in terrestrial rocks were performed only in 1986 by Kurz and by Craig and Poreda. Later, Marti and Craig (1987) reported cosmic-ray produced neon in summit lavas from Maui. More data on cosmogenic helium and neon were reported by Staudacher and All¿gre (1991) on ultramafic nodules from Asia. The absolute production rate of cosmic-ray produced helium has been determined by Kurz (1986, 1987) in olivine rich basalts from Hawaii with known K-Ar or 14C ages. The resulting 3Hec production rate is 3.72¿10-18 cm3 STP/g/a. This allows cosmogenic 3He to be used to determine cosmic ray exposure ages of surface samples. For neon, no such absolute production rate has yet been determined. In order to develop a complementary dating method using cosmogenic 21Ne, Staudacher and All¿gre (1991) measured the cosmogenic 3He/21Ne ratio in ultramafic nodules. Their value was 1.4, which is significantly smaller than the value of 3.5, obtained in this work. Here we discuss the cosmogenic 3He/21Ne ratio in view of new noble gas data on olivine separates of oceanites from R¿union Island and on ultramafic nodules from Mongolia. ¿ American Geophysical Union 1993