The p ha e diagrall\ of the uranium-plati num system \\'as constru cted from data 0 ' )-tained by therma l a na lysis, metallogmphic examina tio n, and X -my diffmction. Th e syste m is characle rized by foUl' intermetalli c co mpounds: U P t, formed pe rilcctoidall.v at, 9(j ] ° C; UPt2, fOfmed perilectically at 1,370° C; UPt3, melting congru enLl. \· at J ,700° C; and U P ts, formed perilectically at, : 1 ,460° C. One eu tectic occurs at 1,005° C and 12 a/o platinu m, and a second at 1,345° C and 87.5 a/o pla tinum. The m aximum solubiliti es a rc .. L5 a/ o u mnium in p latinum and 5 a/o plat inum ill gamma-uranium . Platin um lowc rs Lhe /l:a ll1m a-bl'la lImni1l111 transformalion to 705° C an d the bet.a-alpha transformat ion to . 589° C .