Extremely high-purity InP has been grown in an atmospheric-pressure MOCVD reactor over the unusually large temperature range from 575-700°C. The apparent purity of the material was enhanced by the incorporation of atomic hydrogen. At 650°C, a temperature at which many device structures are grown, a 77 K electron mobility of 190 000 cm2 V-1 s-1 was obtained with an electron concentration of 1.6 × 1014 cm-3. Removal of the hydrogen resulted in a decrease in the electron mobility and an increase in the electron concentration. After removal of the atomic hydrogen, samples grown at 650°C had 77 K electron mobilities of approximately 140 000 cm2 V-1 s-1 at an electron concentration of approximately 3.6 × 1014 cm-3. Analysis of the temperature dependence of the electron mobility indicates that the atomic hydrogen, which comes from the thermal decomposition of the phosphine on epilayer cool-down, neutralises both donors and acceptors. The incorporation and removal of hydrogen does not affect the optical characteristics of the material as measured by photoluminescence and far-infrared photoconductivity.