The first studies of the effect of neptunium doping on the quadrupolar ordering transitions of UPd3 have been made using heat capacity measurements. Here we report details of the heat capacities of 1xNpxPd3 with x 1:4 0, 0:02, 0:05 and ThPd3, a non-magnetic analogue, measured under identical conditions for T 1:4 22300 K. Whilst the heat capacity for x 1:4 0:02 is qualitatively similar to that of pure UPd3, the heat capacity for x 1:4 0:05 is significantly different with the transitions suppressed to below 4K. Measurements on U0:98Np0:02Pd3 in fields up to 9T show that the transition temperatures increase in field, indicating that a 2 Np doping does not destroy the quadrupolar order. The much increased value of Cp=T at T 1:4 2K in these doped samples either suggests these are heavyfermion systems or that there are further transitions below T 1:4 2K. ; JRC.E.6-Actinides research