UPtSn is known as a semimetal with a bandgap in the electronic density of states. We report the results of measurements of the cubic lattice parameter a , coefficient of thermal expansion f , magnetic susceptibility h , magnetization † , specific heat C and electrical resistivity „ . We give arguments that this compound is antiferromagnetically ordered with T N = 35 K, although this is not confirmed by neutron diffraction. For carefully annealed samples of UPtSn we provide a (...) phenomenological description of electron transport properties in terms of the fact that the temperature-dependent bandgap is closed at T = 0 K. Results of electrical measurements on the isostructural compounds ThPtSn and ZrPtSn provide evidence for bandgap formation in these two compounds as well. (shrink)