By alloying boron with RPd3 (R=rare earth) compounds, new ternary alloys of the formula RPd3Bx (0 ≤x ≤ 1) have been prepared. The parent RPd3 compounds crystallise in the cubic AuCu3 type structure. The addition of boron does not change the structure but results in an expansion of the lattice. Therefore, it is likely that the small boron atoms occupy the vacant body centred position in AuCu3 type structure. It is also observed that compounds of the composition RRh3B can be formed in the cubic structure for all rare earths R though the parent RRh3 compounds exist only for R=Ce (AuCu3 type) and La, Sm, Nd and Gd (all hexagonal CeNi3 type). This points out the role of boron in stabilising new crystallographic phases. The results of susceptibility measurements on some of the RPd3B and RRh3B compounds are presented. In particular, it is noted that while GdPd3 orders antiferromagnetically withTN=6 K, GdPd3B does not order magnetically down to 4.2 K.