Pure platinum, together with dilute alloys of platinum (with either oversized or undersized impurities), were irradiated with fast neutrons (> 0,1 MeV) at 4,4 K. The resultant production curves of the alloys were significantly higher than those of the pure metal and deviated strongly from a linear function, even at relatively low doses. Pre-doping of the samples with 400 K irradiation-induced defects produced a notable decrease in the comparative production curves. Existing theories which regard the observed enhancement of resistivity during irradiation as being due to deviations from Matthiessen's Rule, seem inadequate in this case, whereas a model proposing actual enhanced defect production due to the presence of impurities seems more applicable.