H solubility in Zr was determined as a function of temperature and H pressure from 600 deg to 900 deg C. The Zr wire 0,015-in. diam contained Hf 2. 5-3.0, Fe 0.04, O 0.03, and N o.01. The commercial H was purified by passing over shredded 5 platinized asbestos heated to 225 deg C. and through a trap at liquid-N temperature. The H solubilities at 1 atm decreased from 65.9 to 51.6 at.- as the temperature increased from 600 deg to 900 deg C. Partial molal heats and entropies of solutions for molecular H in Zr-H solid solutions were - 39.6 kcalmol and from -30.2 to -36.4 calmoldeg, respectively, from 39.4 to 62.0 at.- H. The equilibrium-H pressures for different H compositions and temperatures are tabulated. Isothermal pressure-volume curves, isothermal pressure-composition log plots, partial phase diagram of the Zr-H system, and pressure-temperature curves for concentrations from 39.4 to 63.1 at.- H, are presented. The binary-phase diagram was correlated with previous x-ray work with the system. The phase diagram indicated a new phase delta between 59.4 and 61. 0 at.- H, and the Zr-rich boundary delta-phase is invariant with the temperature. The delta-phase appeared to be separated from the epsilon-phase by a narrow 2-phase field which is indirectly established. The boundary compositions were from 49.0 to 52.2 and from 58.9 to 59.6 at.- for alpha delta and beta delta 2-phase fields, respectively, and temperatures from 700 deg to 875 deg C. Solubilities for a H pressure of 1 atm were about 10 higher than those previously measured.