Heat-capacity measurements have been made on UP and UP1.35 from 11 to 320°K and values of the standard thermodynamic functions are tabulated. The Cp curve for UP shows a pronounced, sharp anomaly at 22.5°K and also an expected anomaly at 121°K, which corresponds to antiferro-magnetic ordering of the unpaired electrons at the Néel temperature. The origin of the former has not been established, although it may correspond to a transition in the electronic ground state. The entropy increments associated with these anomalies are S22.5°= 0.45 cal deg.–1 mole–1 and S121°= 0.74 cal deg.–1 mole–1. U3P4 shows a Cp anomaly at 136.5°K for which S136.5°= 0.51 cal deg–1. mole–1. This effect corresponds to ferromagnetic ordering of the unpaired electrons at the Curie temperature. The relationship between the entropy increments and the ordered magnetic moments is discussed briefly.