EuPt5, TmPt5, and TmPt3 were prepared by reaction of the gaseous lanthanides with Pt at 1200, 1300, and 1500 degrees C respectively. Structural investigations established that the former two crystallize in CaCu5-type related superstructures, the details being still under investigation. Eu-151 Mossbauer spectroscopy and magnetic susceptibility measurements revealed that EuPt5 is a mixed-valent europium alloy containing both trivalent (Eu[4f(6)]) and intermediate-valent Eu, the latter as a dynamic mixture of the [4f(6)] and [4f(7)] configurations. The magnetochemical analysis of TmPt3 (AuCu3-type structure) on the basis of a crystal field/molecular held model disclosed trivalent Tm[4f(12)] with a singlet crystal field ground state and the absence of magnetic ordering (for T greater than or equal to 1.7 K).