The spin relaxation time T-1 for short-lived beta emitters O-13 and Mg-23 implanted in Pt have been measured for the first time; T1T(O-13) = 2.90 +/- 0.65 Ks and T1T( Mg) = 1665 +/- 140 Ks. The Knight shift for O-13 in Pt was measured at 300 K to be K(O-13) = +(4.23 +/- 0.14) x 10(-3). In the case of O-13, the Knight shift is unusually large and the relaxation time is unusually fast compared with other interstitial impurities in Pt. A KKR band-structure calculation reproduces the present large Knight shift fairly well.