Platinum group metal additions made to thick films of YBCO have induced significant improvements in the superconducting properties, in particular critical current densities (J c ). Values in excess of 7 10 3 A cm - 2 at 77 K and zero applied field have been measured. Optical and transmission electron microscopy have shown a homogeneous distribution of sub-micron sized, and larger highly anisotropic 211, believed to result from a reaction between Pt and YBCO to create nucleation sites for 211 precipitates. Indirect supporting thermal analysis evidence for this reaction is presented. An increased density of dislocations associated with the 123/211 interface suggests that refined 211 precipitates may act as heterogeneous nucleation sites for flux pinning defects. Similar effects have been observed for additions of other platinum group metals (Ph, Pd).