Experimental measurement of nuclear heating rates was carried out in a simulated D-T fusion neutron environment from 1989 through 1992 under the U.S. DOE/JAERI collaborative program at the Fusion Neutronics Source Facility. Small probes of materials were irradiated in close vicinity of a rotating target. A sophisticated microcalorimetric technique was developed for on-line measurements of total nuclear heating in a mixed neutron plus photon field. Measurements with probes of graphite, titanium, copper, zirconium, niobium, molybdenum, tin, tungsten, and lead are presented. These measurements have been analyzed using the three-dimensional Monte Carlo code MCNP and various heating number/kerma factor libraries. The ratio of calculated to experimental (C/E) heating rates shows a large deviation from 1 for all the materials except tungsten. For example, C/E's for graphite range from 1.14 (σ = 10%) to 1.36 (10%) for various kerma factor libraries. Uncertainty estimates on total nuclear heating using a sensitivity approach are presented. Interestingly, C/E data for all libraries and materials can be consolidated to obtain a probability density distribution of C/E's that very much resembles a Gaussian distribution centered at 1.04. The concept of “quality factor” is defined and elaborated so as to take cognizance of observed uncertainties on prediction of nuclear heating for all the nine materials.