Changes in the electronic structure of platinum-3d transition single-crystal alloys (Pt(1-x)M(x) with M = Fe, Co, and Ni) are studied as a function of composition, order and nature of the 3d metal. These changes are detected by using synchrotron radiation to analyze the absorption edges. Both the Pt L(II) and L(III) edges and the 3d metal K edge exhibit correlated changes, which are most sensitive to the minority element in the alloy. The modifications on the Pt L(II) and L(III) edges are interpreted as resulting from a variation of the number of holes in the 5d band, corresponding to an electron transfer to platinum from the 3d metal. The corresponding changes observed on the 3d metal K edge point to a population rearrangement between the probed levels originating from the atomic 3d, 4s, and 4p levels. An effect of ordering has also been observed in the Pt-Co alloys the magnitude of which is greater at the Co K-edge for the lowest concentration of this element. Finally, we compare our results to available calculations and experimental results obtained by other techniques.