The photon fluence due to isotropic photon point sources in air has been calculated with a Monte Carlo code that accounts for photon absorption, Compton scattering, annihilation, and bremsstrahlung. Kerma buildup factors have been determined for ten energies in the 0.05- to 10-MeV range and for 72 distances in the 0.15- to 10-mfp range. The results agree with the moments calculations of Chilton, Eisenhauer, and Simmons within 5%, except for low energies and great penetration depths, where the buildup factors differ by more than 20%. This deviation may be due to the use of different cross-section data. The buildup factors have been analytically approximated by a polynomial in E−1 and µr with an accuracy of better than 5% for all 720 data points.