Previous heat flow measurements have suggested an increase of 16 ± 9 mW/m2 in the vicinity of Ocean Drilling Program (ODP) Leg 149 Site 900 (Louden and Mareschal, 1996) and in the region immediately landward along profile Lusigal 12 (Louden et al., 1997) relative to values farther seaward. One possibility is that this increase could indicate enhanced values of radiogenic heating within the basement rocks. However, measurements of radioelements on metagabbro samples from Site 900 (Louden and Mareschal, 1996) were too low to explain this increase. To investigate whether the Site 900 samples were indeed fully representative of the upper crust in this region, new measurements of radiogenic heat production from near Site 900 were made on additional samples cored at Sites 1067 and 1068 during Leg 173.