The abundances of U and Th in 19 achondrites and two pallasite olivines have been measured by radiochemical neutron activation analysis. Brecciated eucrites are enriched relative to chondrites in both elements by factors between 10 and 20, perhaps as a result of a magmatic differentiation process. Two unbrecciated eucrites are far less enriched, possibly due to their origin as igneous cumulates. The diogenites Johnstown and Shalka contain approximately chondritic levels of U and Th, but Ellemeet is 10 times lower. The abundances in three howardites are in good agreement with those expected from major element data for a mixing model with eucrite and diogenite end members. The high O 18 basaltic achondrites Nakhla, Shergotty and Angra dos Reis have a range of U and Th abundances similar to the brecciated eucrites and howardites, but have systematically higher Th/U ratios. The Bishopville aubrite has U and Th abundances and Th/U ratios similar to those of several enstatite chondrites, suggesting a genetic relationship. The Norton County aubrite has a low Th/U, similar to that observed in recrystallized and metamorphosed terrestrial ultrabasic rocks, indicating a more complex history. Pallasite olivines have low U and Th contents (0.5.4 ppb and 1.4.3 ppb, respectively) similar to those in terrestrial dunites. The Goalpara ureilite has very low U (<0-6 ppb) and Th (2.7 ppb) abundance consistent with an origin from carbonaceous chondrites by partial melting.